feat: support less each function

[shellscape]

Which issue # if any, does this resolve?

Please check one:

• New tests created for this change
• Tests updated for this change

This PR:

• Adds new API
• Extends existing API, backwards-compatible
• Introduces a breaking change
• Fixes a bug

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This PR fixes #121 by adding relatively naive support for the new each function in LESS. each is relatively unique, as it's the only function used at the root level, outside of a ruleset. While this change doesn't do anything special with the params, it allows the parser to continue on without throwing an error.

The result is an AtRule with a function: true property, and params property which contains everything between the first and last, open and closed parenthesis.

In the future we might examine how to parse and present the params for each in the node.

[codecov-io]

Codecov Report

Merging #127 into master will increase coverage by 0.35%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #127      +/-   ##
==========================================
+ Coverage   95.74%   96.09%   +0.35%     
==========================================
  Files           8        8              
  Lines         188      205      +17     
==========================================
+ Hits          180      197      +17     
  Misses          8        8

Impacted Files	Coverage Δ
lib/LessStringifier.js	87.5% <100%> (+0.54%)	⬆️
lib/LessParser.js	98.92% <100%> (+0.22%)	⬆️

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[jwilsson]

I like this idea, putting everything into params, better too. I'd argue that everything are parameters and parsing that should be easy enough if someone wants to parse it further.

Code LGTM too.

[shellscape]

🎉