[lang] Add the annotation @FiredEvent.

This annotation is generated from the "fires" keyword.
With this annotation, we are able to make some tests (unreachable codes,
...) from definitions that are outside the current SARL file.

see #202

Signed-off-by: Stéphane Galland <galland@arakhne.org>
[lang] Add the @FiredEvents and @EarlyExit annotations

The @FiredEvents annotation permits to mark the Java functions with the
SARL events that are specified with the "fires" keyword.

The @EarlyExit annotation is used for marking the methods that never
return. In this case, the SARL validator output a "Unreachable code"
error for any statement following the call to a marked method.

The fired "Destroy" event (marked by @FiredEvent) is used for marking
the method with @EarlyExit.

see #202

Signed-off-by: Stéphane Galland <galland@arakhne.org>