Replace Liquid grammar with a more recent & complete one

[macournoyer]

Replace the Liquid grammar with a more recent & complete one.

Description

The current Liquid grammar doesn't support much of the Liquid syntax.

This PR replaces it with a more complete one: https://github.com/macournoyer/language-liquid/tree/master/grammars

Checklist:

• I am associating a language with a new file extension.

  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am adding a new language.

  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a syntax highlighting grammar: https://github-lightshow.herokuapp.com/
  • I have updated the heuristics to distinguish my language from others using the same extension.

• I am fixing a misclassified language

  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am changing the source of a syntax highlighting grammar

  • Old: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_format=auto&grammar_url=https%3A%2F%2Fgithub.com%2Fbastilian%2Fvalidcode-textmate-bundles%2Fblob%2Fmaster%2FLiquid.tmbundle%2FSyntaxes%2FHTML%2520Liquid.plist&grammar_text=&code_source=from-url&code_url=https%3A%2F%2Fgist.githubusercontent.com%2Fmacournoyer%2Ff13cd82019f0c58d60adb1c68b429207%2Fraw%2Fab85c61f25354d22848522f9a22868c20bebb10a%2Ftheme.liquid&code=https%3A%2F%2Fgist.githubusercontent.com%2Fmacournoyer%2Ff13cd82019f0c58d60adb1c68b429207%2Fraw%2Fab85c61f25354d22848522f9a22868c20bebb10a%2Ftheme.liquid
  • New: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_format=auto&grammar_url=https%3A%2F%2Fgithub.com%2Fmacournoyer%2Flanguage-liquid%2Fblob%2Fmaster%2Fgrammars%2Fhtml%2520%28liquid%29.cson&grammar_text=&code_source=from-url&code_url=https%3A%2F%2Fgist.githubusercontent.com%2Fmacournoyer%2Ff13cd82019f0c58d60adb1c68b429207%2Fraw%2Fab85c61f25354d22848522f9a22868c20bebb10a%2Ftheme.liquid&code=https%3A%2F%2Fgist.githubusercontent.com%2Fmacournoyer%2Ff13cd82019f0c58d60adb1c68b429207%2Fraw%2Fab85c61f25354d22848522f9a22868c20bebb10a%2Ftheme.liquid

• I am updating a grammar submodule

• I am adding new or changing current functionality

  • I have added or updated the tests for the new or changed functionality.

• I am changing the color associated with a language

  • I have obtained agreement from the wider language community on this color change.
    • [URL to public discussion]
    • [Optional: URL to official branding guidelines for the language]