Merge pull request #82 from Intrepidd/master

Allow overwriting of events, can be very useful with inheritance
fixed travis ci icon
supporting nested AR transactions
Ruby 1.8 syntax
Merge pull request #86 from ozeias/master

Supporting nested AR transactions
version bump to 3.0.21
Include basic information about Mongoid usage
Merge pull request #89 from jxa/patch-1

Include basic information about Mongoid usage
fix #88 (wrong number of arguments for transaction method)
version bump to 3.0.22
Allow a block to be called when running a transition