add shortcut '&&=' for preprocessing values only when they exist.
Merge pull request #255 from TalkativeTree/preprocess-value-shortcut

add shortcut '&&=' for preprocessing values only when they exist.
Add rules about trailing commas.

Can occur in literals and method definitions/calls. These rules were discussed in https://github.com/bbatsov/rubocop/issues/713
Merge pull request #258 from jonas054/trailing_comma

Add rules about trailing commas.
Remove trailing comma rule for method definitions.

Trailing comma in a method definition is a syntax error.
In method calls it is allowed starting with Ruby 1.9.
Merge pull request #259 from jonas054/trailing_comma

Remove trailing comma rule for method definitions.
Add contribution guidelines
Add Vietnamese version link
Merge pull request #261 from scrum2b/for_pull_master

Add Vietnamese version link
Merge pull request #253 from Chakaitos/master

Add section on How to Contribute
Add guideline for using explicit block argument
Merge pull request #260 from tkareine/use-named-block-to-avoid-writing-additional-block

Use named block argument to avoid writing additional block in method implementation
Fix typo in introduction
Merge pull request #266 from jvirtanen/fixes/introduction

Fix typo in introduction