Ignore dev.pl
Clean up documentation
Change semantics of signal/2 when no handlers exist

signal/2 used to fail if there were no matching handlers.  That's like
saying, "the Titanic was fine because nobody saw its signal flares."
Obviously, if nobody saw the flare, we must do something more drastic to
get attention.  Throwing an exception is the obvious choice.

For use cases where an exception is too dramatic, we now provide
signal/3.
Add add_handler/2 and rm_handler/1

These predicates can be helpful when multiple goals need the same
handlers.
Release v0.1.0