update document link version in DEVELOPMENT.md
Merge pull request #2803 from loveky/master

update document link version in DEVELOPMENT.md
note code of conduct in contributing.md
rubygems 2.2.1
rubygems 2 still supports 1.8!
lazy load similarity detector
break out UI::RGProxy
break out UI::Shell
autoload is at least more consistent
add silence to quiet UI

fixes #2807
realign public interfaces of UI and Shell
extract UI::Silent
allow single quotes in config values

fixes #2469
ruby 1.8 doesn't add quotes to values
Improved resolver significantly by trimming the search space
Fix #2813: Ignore self dependency
Merge branch 'master' of github.com:Who828/bundler
Fixed the failing spec in Ruby 1.8.7
Remove code duplication and add comments for readability
Resolver now looks exiting gem parent to resolve more effectively