Fix migration example in README
Merge pull request #62 from Nitrodist/master

Fix migration example in README
removed unneeded method (reading the current state for persisted states is already handled)
one file per test model class
fixed tests for Mongoid
shorten the persistence loading stuff a bit
using Ruby method resolution to read the current state
no need for ReadState anymore
keep it simple
no need for WriteState mixin anymore (to keep adding persistence simple)
no need for WriteStateWithoutPersistence mixin anymore (to keep adding persistence simple)
just a comment
:rubygems is insecure
testing mongoid for Ruby >= 1.9.3 again
supporting instance level inspection for states
supporting instance level inspection for states (including permissible state, see issue #54)
corrected heading for inspection
added pry (but not using it)
updated the code climate badge
test coverage via coveralls