added support for Arturo programming language

[drkameleon]

Issue #, if available:

Description of changes:

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

Merging #4081 into master will decrease coverage by <.01%.
The diff coverage is 62.5%.

@@            Coverage Diff             @@
##           master    #4081      +/-   ##
==========================================
- Coverage   70.34%   70.33%   -0.01%     
==========================================
  Files         519      521       +2     
  Lines       50855    50911      +56     
  Branches     9583     9586       +3     
==========================================
+ Hits        35774    35809      +35     
- Misses      15081    15102      +21

Impacted Files	Coverage Δ
lib/ace/mode/arturo.js	100% <100%> (ø)
lib/ace/mode/arturo_highlight_rules.js	48.78% <48.78%> (ø)

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[whazor]

Hi, thanks for your contribution, and our apologies for not replying earlier.

Could you please rebase and add tests via highlight_rules_test.js (readme).

Thanks again!