Sphinx domains

• Adds support for Sphinx domains.
  • The following directives will now get language specific syntax highlighting:
    • .. cpp:xyz::
    • .. c:xyz::
    • .. py:xyz::
    • .. js:xyz::
• Removed auto indent when jumping from a *** based heading underline
• Now requiring at least one letter, number or underscore for VS Code to consider a chunk of text a word
  • Prevents VS Code from suggesting autocompletions for --- heading underlines.
• Support for all markup inside non-literal directives.
• Minor fixes to detection for comments, inline markup and directive indentation.