upgrade gems
use released version of appraisal
upgrade gemfiles for appraisal
split database.yml files for mongoid 2/3
Merge remote-tracking branch 'origin/master' into mooremo-master
add changelog notes for #9
split out CONTRIBUTING file
change exception class to be Mongoid::Locker::LockError - closes #8
add more testing instructions
drop testing support for Rubinius 1.8-mode
link to rdoc for #with_lock options
add Code Climate badge
Relax dependency on Mongoid 3.2.x.
Merge pull request #11 from dblock/mongoid-3.2-dependency

Relax dependency on Mongoid 3.2.x.