Added the Ability to Create Events Using Notation

[hishamabri]

Thanks for the great tool!

Just a simple addition that allows the addition of events using notation.
Example from the README file:

[inboxStateMachine addEventWithNotation:@"Deleted->UnDelete->Read"];

Which adds an event named 'UnDelete' for transitions from the Deleted state to the Read state.
I found this useful and more visual in my opinion.

The user can comma separate the source states:

[inboxStateMachine addEventWithNotation:@"Read,Deleted->Mark as Unread->Read"];

Added a few tests to accomodate the new changes.
Hope everything is up to standard.

Cheers,
Hisham

[hishamabri]

Not sure why Travis CI keeps failing with:
The command "gem install cocoapods" failed and exited with 1 during .