Add FSM external events

[Tonidotpy]

The event code generation is disabled by default and can be enabled with the --event flag
The generated code can be used to trigger an event from outside the FSM and check whether an event has fired or not

[pbosetti]

Cool. Can you also add an example graphviz supporting events?

I'd also bump the minor version number rather than the patch level.

[Tonidotpy]

I changed the event code generation, now it is enabled by default and can be used via the is_event_triggered and event_trigger functions.
The new type event_data_t can also be used to pass custom data when the event is fired.