Add Jekyll::LiquidExtensions.lookup_variable

[parkr]

To use, just include Jekyll::LiquidExtensions as you please:

class SayHi < Liquid::Tag
  include Jekyll::LiquidExtensions

  def initialize(tag_name, markup, tokens)
    @markup = markup.strip
  end

  def render(context)
    "hi #{lookup_variable(context, @markup)}"
  end
end

Fixes #2071.

/cc @gjtorikian

[gjtorikian]

Sweet!

[parkr]

@gjtorikian Is this an OK place to put it? Only other place I would consider is a Jekyll::LiquidExtensions module that people could include into their tags.

[parkr]

Using a module instead of Jekyll::Utils. Yay for one more module!