Moved yard gem under common group development and documentation in Gemfile

- While running 'bundle' with bundler version 1.5.1 command following message was observed
  Your Gemfile lists the gem yard (>= 0) more than once.
  You should probably keep only one of them.
  While it's not a problem now, it could cause errors if you change the version of just one of them later.
- This commit adds 'yard' gem to common group of development and
  documentation to remove that message
Redis is no longer a default travis service
Travis: Rubinius (rbx) 1.9 is dead, long live rbx.
Merge remote-tracking branch 'prathamesh-sonpatki/move-yard-to-common-group'
Merge pull request #1162 from tyre/master

Add Resque.configure documentation to README
add :log_file configuration option and update README