Highlight ALAN: Add Block Comments Support

[tajmone]

Our custom ALAN syntax for Highlight doesn't cover the new block comments that will be available with ALAN Beta8.

• [x] Update ALAN syntax for Highlight to support block comments.
  • [x] Add new tweaked syntax to repository (currently relying on official package).
• [x] Update Sass theme for ALAN to cover the com class for block comments.
• [x] Update developer test docs in _dev/styles-tests/:
  • [x] Remove warning for Highlight not supporting block comments.
• [x] Submit updated syntax to Highlight repository.

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Ongoing implementation work can be tracked on the ALAN Testbed project:

• https://github.com/alan-if/Alan-Testbed/tree/master/syntax-hl/Highlight

but so far I've been struggling to implement block comments supports due to Highlight quirks in precedence order of matching RegExs — but I think I've found a fix for this via custom hooks code, just need to sit down and work on it.

[tajmone]

Block Comments Implemented

I've updated the Highlight syntax for ALAN to cover block comments, which can be found in the ALAN Testbed:

• https://github.com/alan-if/Alan-Testbed/tree/master/syntax-hl/Highlight
• HTML LivePreview of sample.html

Now I only need to add the new syntax to this repo, update the Sass themes to cover block comments. Before we were using the native ALAN syntax that ships with HL, but now I'll be adding our custom syntax, so that we can start using it before it's included in the next HL release package (of course, I'll submit it to HL too). This will also simplify adding other custom syntaxes, e.g. for the EBNF blocks.