Update CONTRIBUTING.md

Add @arthurnn for code review
Convert legacy tab indentation to spaces and remove trailing whitespace from all lines
Don't render blank blocks
Some tests for whitespace collapsing
More tests for whitespace collapsing
Clean up whitespace collapsing a bit
Cycle tags are never blank
Clean up whitespace collapsing
Update History.md
Merge pull request #219 from Shopify/indent_and_trailing_ws_cleanup

Convert legacy tab indentation to spaces and remove trailing whitespace ...
Merge branch 'master' into dont_render_blank_blocks

Conflicts:
	lib/liquid/tags/cycle.rb
	lib/liquid/tags/increment.rb
Fix some typos in comments
Merge pull request #220 from coding46/master

Fix some typos in comments
Changes not empty? to any?
Merge pull request #221 from d-Pixie/master

Changes not empty? to any?
Make sure include tags are never blank
Merge branch 'master' into dont_render_blank_blocks

Conflicts:
	lib/liquid/tag.rb
Add blank test for case tags
Merge pull request #218 from Shopify/dont_render_blank_blocks

Dont render blank blocks
Fix some blank tests