Merge branch 'release/0.2.6' into develop
Added CONTRIBUTING.md.
Updated TODO list.
Updated TODO list.
Merge branch 'develop' of github.com:trema/pio into develop

Conflicts:
	pio.org
Enabled rubocop.
Added utf-8 encoding comments for 1.9.3.
Enable travis CI for 1.8.7.
Fixed rubocop's EmptyLines warnings.
Fixed DefWithoutParentheses warnings.
Fixed rubocop's Alias warnings.
Fixed rubocop's AndOr warnings.
Fixed rubocop's Blocks warnings.
Fixed rubocop's BracesAroundHashParameters warnings.
Fixed rubocop's ClassLength warnings.
Fixed rubocop's CollectionMethods warnings.
Fixed rubocop's Documentation warnings.
Fixed rubocop's FavorSprintf warning.
Enforce hash rockets style.
Fixed rubocop's IfUnlessModifier warnings.