Add keyword arguments for Liquid shortcodes.

[dawaltconley]

Fixes #1263. This removes moo and switches the argument lexer/parser for Liquid shortcodes to liquid-args, to support keyword arguments with output mirroring Nunjucks kwargs.

This includes some breaking changes in how Liquid shortcodes handle the whitespace in between arguments. With liquid-args, whitespace can be any number of space, tab, newline, or carriage return characters ([ \t\n\r]), and will allow a comma at the beginning of the whitespace. That means that the following tags will parse correctly:

{% shortcode arg1, arg2, arg3 %}
{% shortcode arg1 arg2 arg3 %}
{% shortcode arg1,arg2,arg3 %}
{% shortcode arg1    arg2, 
    arg3 %}

But the following, which was previously supported, will break:

{% shortcode arg1,,arg2,,arg3 %}
{% shortcode arg1 , arg2 , arg3 %}
{% shortcode arg1 ,arg2 ,,arg3 %}

There are also some changes to how shortcodes parse numbers and dot-notation variable names. The previous moo parser would accept numbers like 10...78 and variable names like ..foobar.baz. These were passed to the Liquid engine, which would throw an error for invalid Liquid. The liquid-args parser rejects these before passing to the engine. This shouldn't cause breaking changes but could affect error handling in some cases.

Basically the same as #1269, but updated to the latest version of 11ty.

[mphstudios]

@zachleat has there been any thought about merging this change or perhaps additional work to make the args lexer a configurable template engine option?

[zachleat]

Closing this one per the comment left over at #1263. #1263 (comment)

Again, I’m sorry this didn’t make it!