Further Node-related config related to database names

[brettz9]

The following are further todos related to #274 which which are lower priority since if someone really needs the Unicode, they can override escapeDatabaseName themselves (though it'd admittedly be better to bake in an option) and the third issue is not really bug-related:

• Striking out as may not be needed: Provide an option for (Node) users to escape (and potentially unescape) upper-case letters when mapping case-sensitive IndexedDB database names to SQLite database file names since a number of modern Unicode file systems that might host such SQLite database files are nevertheless case-insensitive and thus a system allowing arbitrary (finite-length) strings could inadvertently provide a conflict if relying purely on string equality. Currently we are only escaping A-Z.
  • Case-insensitivity may only actually be a problem for ASCII at least in Windows. I wonder if the other modern systems referenced above have similar issues.
  • If we do find a need for it:
    • If we escape other characters, we'd need to use another numbered escape sequence like ^2 or ^3.
    • If using a code point escape sequence, we'd need to indicate a different length following like 4 or 6 (the other characters will be more than 2 hex digits)
    • We could alternatively map to a form of lower-case
      • toLocaleLowerCase would risk portability problems, and though toLowerCase is Unicode-aware (apparently using the C and S case foldings), we want not only locale-independent and moderately human-friendly forms for escaping, but also round-trippable ones so that if a database file is transported to another system, it can be unescaped and understood.
      • The repository for the latest Unicode (currently unicode-9.0.0/Case_Folding) would help a lot with retrieval of the case mappings (Our file-system-safe escape character, ^ could be used along with the lower-case letter as well a number (where needed) to avoid a potential round-tripping conflict (e.g., with ^k1 and ^k2 to escape upper case K and the Kelvin sign, respectively, as they would otherwise both map back to the letter "K", or perhaps better for readability ^k and ^3k2 with 3 indicate a non-ASCII (or lower code point) case mapping and 2 indicating it was the 2nd possible conflict; this could become fragile with new Unicode versions, however.)
      • If adding this support (via XRegExp if Babel/ES doesn't support case matching by then), we may as well also change our hard-coding of Unicode ID Start, etc. to use XRegExp's also.
• Perhaps we should actually be more concerned about escaping characters which might be normalized by NFD in the MacOS if this is accurate: https://en.wikipedia.org/wiki/Filename#Unicode_interoperability as that could also provide uniqueness issues
  • This could be made easier with building mappings based on String.prototype.normalize and/or the polyfill
  • Also see unicode-9.0.0/Binary_Property/Expands_On_ (NFC/NFD/NFKC/NFKD); might just escape NFD-expanding ones for compatibility with MacOS
• Offer config for Node users to leverage node-sqlite3's (and consequently node-websql's) ability to use empty string or ":memory:" in-memory databases, including "file::memory:..." URLs for creating temporary databases (should also get this latter type documented on node-websql). We might consider keeping track of memory databases to allow closing them via deleteDatabase (though would need to return some kind of unique ID)? Add close(function (err) {}) callback to node-sqlite3 (websqlOpenDatabaseDb._db.close()) calls; https://github.com/mapbox/node-sqlite3/wiki/API#databaseclosecallback ; closing will also auto-delete empty string temp. dbs per https://sqlite.org/inmemorydb.html (also to call when deleting or closing/finishing connection and reporting errors as per Utilize SQLite close #295 )
• Option in Node to delete the actual database file as well and delete __sys__.sqlite database if empty (may need queue (or wholly sync behavior--see Provide optional Node support for accurate task/microtask behavior #296 ) to avoid errors after deleteDatabase followed by open) whether after deleting database or aborting an upgrade

[brettz9]

Tracking the remaining issue for the new package at #11