Add more configuration options to TryExamples directive and add documentation

[steppi]

This PR updates adds more flexible configuration for the TryExamples directive, fixes some small bugs, and adds documentation.

New options include

• :button_text: for changing the text of the button for switching from rendered examples to a notebook.
• :button_hover_css: for specifying the css properties to give to the button when the user hovers over it,
• :button_position_vertical: one of top or bottom specifying vertical placement of the button with respect to the examples block covered by the directive.
• :button_position_horizontal: one of left, right, or center, analogous to above.
• :min_height:, the minimum height to give the iframe container for the notebook. By default, the height is the same as the height of the rendered examples block the container replaces. For very small examples blocks, this yields an unusably small notebook. :min_height: helps with this edge-case.

I noticed that the TryExamples directive had stopped working following the update to Jupyterlite 0.2 due to changes in paths; this has been fixed.

I've also fixed a bug that causes math blocks within markdown cells to be skipped if there is no additional content after them.

I've added documentation for the directive and how it can be configured. I note that one needs to make sure that the version of the package in your Jupyterlite kernel needs to match the version of the package you are documenting, but did not elaborate on this, because I haven't solved this problem yet. I've been testing this on the latest SciPy release. Eventually it would be nice to be able to use the directive in dev docs, and when that get's figured out, I'll add more information to the documentation.

[steppi]

I just added conversion of sphinx format links link text <url> into markdown format [link text](url) after noticing the link didn't render correctly in the example in the docs.

I'll work on getting the SciPy docs published at https://steppi.github.io/scipy built against this branch. I ran out of circle ci free credits, so it's not as simple as a push. I'll figure something out. Things look good locally though.

[martinRenou]

Thanks a lot! Will try to give it a review by the end of the week

[steppi]

Docs from this branch are up at https://steppi.github.io/scipy

you can find a specific example here https://steppi.github.io/scipy/reference/generated/scipy.integrate.tplquad.html#scipy.integrate.tplquad

[martinRenou]

LGTM!

[martinRenou]

Released!

[steppi]

Awesome! Thanks @martinRenou! Hoping to have this shipped in SciPy’s docs soon.