Add liquid to languages.yml.
Add Liquid samples.
Remove HTML+Liquid language.
type can also be "prose"
For now, let's just use a Text-only Liquid lexer.
Update samples.json with Liquid samples.
Add XML, HTML and JSON samples for Liquid.
.st file extension for StringTemplate HTML files

Conflicts:
	lib/linguist/samples.json
Merge pull request #1120 from github/1116-1117-update

1116 1117 update