Bump towncrier from 19.2.0 to 21.3.0 (#577)

Bumps [towncrier](https://github.com/hawkowl/towncrier) from 19.2.0 to 21.3.0.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/twisted/towncrier/blob/master/NEWS.rst">towncrier's changelog</a>.</em></p>
<blockquote>
<h1>towncrier 21.3.0 (2021-04-02)</h1>
<p>No significant changes since the previous release candidate.</p>
<h1>towncrier 21.3.0.rc1 (2021-03-21)</h1>
<h2>Features</h2>
<ul>
<li>Ticket number from file names will be stripped down to avoid ticket links such as <code>[#7](https://github.com/hawkowl/towncrier/issues/007)</code>. (<code>[#126](twisted/towncrier#126) &lt;https://github.com/hawkowl/towncrier/issues/126&gt;</code>_)</li>
<li>Allow definition of the project <code>version</code> and <code>name</code> in the configuration file.
This allows use of towncrier seamlessly with non-Python projects. (<code>[#165](twisted/towncrier#165) &lt;https://github.com/hawkowl/towncrier/issues/165&gt;</code>_)</li>
<li>Improve news fragment file name parsing to allow using file names like
<code>123.feature.1.ext</code> which are convenient when one wants to use an appropriate
extension (e.g. <code>rst</code>, <code>md</code>) to enable syntax highlighting. (<code>[#173](twisted/towncrier#173) &lt;https://github.com/hawkowl/towncrier/issues/173&gt;</code>_)</li>
<li>The new <code>--edit</code> option of the <code>create</code> subcommand launches an editor for entering the contents of the newsfragment. (<code>[#275](twisted/towncrier#275) &lt;https://github.com/hawkowl/towncrier/issues/275&gt;</code>_)</li>
<li>CPython 3.8 and 3.9 are now part of our automated test matrix and are officially supported. (<code>[#291](twisted/towncrier#291) &lt;https://github.com/hawkowl/towncrier/issues/291&gt;</code>_)</li>
<li>When searching for the project, first check for an existing importable instance.
This helps if the version is only available in the installed version and not the source. (<code>[#297](twisted/towncrier#297) &lt;https://github.com/hawkowl/towncrier/issues/297&gt;</code>_)</li>
<li>Support building with PEP 517. (<code>[#314](twisted/towncrier#314) &lt;https://github.com/hawkowl/towncrier/issues/314&gt;</code>_)</li>
</ul>
<h2>Bugfixes</h2>
<ul>
<li>Configuration errors found during command line execution now trigger a message to stderr and no longer show a traceback. (<code>[#84](twisted/towncrier#84) &lt;https://github.com/hawkowl/towncrier/issues/84&gt;</code>_)</li>
<li>A configuration error is triggered when the newsfragment files couldn't be discovered. (<code>[#85](twisted/towncrier#85) &lt;https://github.com/hawkowl/towncrier/issues/85&gt;</code>_)</li>
<li>Invoking towncrier as <code>python -m towncrier</code> works. (<code>[#163](twisted/towncrier#163) &lt;https://github.com/hawkowl/towncrier/issues/163&gt;</code>_)</li>
<li><code>check</code> subcommand defaults to UTF-8 encoding when <code>sys.stdout.encoding</code> is <code>None</code>.
This happens, for example, with Python 2 on GitHub Actions or when the output is piped. (<code>[#175](twisted/towncrier#175) &lt;https://github.com/hawkowl/towncrier/issues/175&gt;</code>_)</li>
<li>Specifying <code>title_format</code> disables default top line creation to avoid duplication. (<code>[#180](twisted/towncrier#180) &lt;https://github.com/hawkowl/towncrier/issues/180&gt;</code>_)</li>
</ul>
<h2>Improved Documentation</h2>
<ul>
<li>The README now mentions the possibility to name the configuration file
<code>towncrier.toml</code> (in addition to <code>pyproject.toml</code>). (<code>[#172](twisted/towncrier#172) &lt;https://github.com/hawkowl/towncrier/issues/172&gt;</code>_)</li>
<li><code>start_line</code> corrected to <code>start_string</code> in the readme to match the long standing implementation. (<code>[#277](twisted/towncrier#277) &lt;https://github.com/hawkowl/towncrier/issues/277&gt;</code>_)</li>
</ul>
<h1>towncrier 19.9.0 (2021-03-20)</h1>
<p>No significant changes.</p>
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</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/twisted/towncrier/commit/eab34611b93a4ba6e3805cd546a674d88dbd43cf"><code>eab3461</code></a> Update NEWS.rst</li>
<li><a href="https://github.com/twisted/towncrier/commit/bd963c351853d8977cd37c501b2b1b85d7cb0217"><code>bd963c3</code></a> add back the newsfragment...</li>
<li><a href="https://github.com/twisted/towncrier/commit/3bf4479562f0cc6ff828fe93fffb94fadc4c731d"><code>3bf4479</code></a> Bump version to 21.3.0</li>
<li><a href="https://github.com/twisted/towncrier/commit/3237ebd09527cecfd758c0fb472a3f5c7ccb1acb"><code>3237ebd</code></a> remove misc section</li>
<li><a href="https://github.com/twisted/towncrier/commit/6eab89476cd4b3849563496c19d07905109c9f61"><code>6eab894</code></a> Correct underlines setting to toml in readme</li>
<li><a href="https://github.com/twisted/towncrier/commit/4143e0ff55177cca5747d18624d614e593ebe3c3"><code>4143e0f</code></a> add 332.misc</li>
<li><a href="https://github.com/twisted/towncrier/commit/05eea3f2240bfebee4522e1c1180893f7a79a509"><code>05eea3f</code></a> Release 21.3.0rc1</li>
<li><a href="https://github.com/twisted/towncrier/commit/2841c12f2e7ebfc40d9cc3228ca468d339225549"><code>2841c12</code></a> Release 19.9.0 (<a href="https://github-redirect.dependabot.com/hawkowl/towncrier/issues/331">#331</a>)</li>
<li><a href="https://github.com/twisted/towncrier/commit/7267fb56e2a34b4f81b4e0005e3f4eeddaa71b2b"><code>7267fb5</code></a> twisted-alike (so similar) automatic publishing on gha (<a href="https://github-redirect.dependabot.com/hawkowl/towncrier/issues/315">#315</a>)</li>
<li><a href="https://github.com/twisted/towncrier/commit/499c8f7990f82d7decd32f139ec7a1c2d1b25719"><code>499c8f7</code></a> use incremental to canonicalize versions for release (<a href="https://github-redirect.dependabot.com/hawkowl/towncrier/issues/329">#329</a>)</li>
<li>Additional commits viewable in <a href="https://github.com/hawkowl/towncrier/compare/19.2.0...21.3.0">compare view</a></li>
</ul>
</details>
<br />


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requirements/towncrier.txt

@@ -1 +1 @@
-towncrier==19.2.0
+towncrier==21.3.0