Add # inline comment tag.

This commit adds a new tag named `#` that behaves like a comment.

Therefore it behaves as you'd expect any tag would work. The difference
with the comment tag is that the comment is in the tag markup and that
there is no block delimiter.

What it looks like in practice:

```liquid
{%- # this is an inline comment -%}
{% # this too is an inline comment %}

{% liquid
  # required args:
  assign product = product

  # optional args:
  assign should_show_border = should_show_border | default: true
  assign should_show_cursor = should_show_cursor | default: true
%}

{% liquid
  # This is a very long comment that spans multiple lines.
  # It looks very similar to what it would look like if you wrote
  # ruby code instead of liquid. But it doesn't have all the clunk
  # of having an open tag and a close tag with so many characters.
%}
```

Co-authored-by: Dylan Thacker-Smith <[email protected]>

lib/liquid.rb

@@ -29,6 +29,7 @@ module Liquid
   WhitespaceControl           = '-'
   TagStart                    = /\{\%/
   TagEnd                      = /\%\}/
+  TagName                     = /#|\w+/
   VariableSignature           = /\(?[\w\-\.\[\]]\)?/
   VariableSegment             = /[\w\-]/
   VariableStart               = /\{\{/