sslot version 0.2

[Lutger]

I've uploaded a new version using the features of D since 0.173. Perhaps 
it is useful to those who want return values and other callable types 
than delegates from objects in their signals:

http://lutger.ifastnet.com

Some changes:
- No need for interface + mixin anymore to manage connections.
- No limit to the number of arguments.
- Slots can be temporarily blocked and unblocked.
- As suggested by Bill Baxter, a signal which doesn't have a return 
value can connect any slot with a return value.
- Better compiler time error messages. I've included Don Clugston's 
meta.nameof for this, I'm sure it has an open source license but I 
couldn't find exactly which one.
- Classes can be injected with the signal code by using a mixin.
A test module is included.

Note that connecting is slightly different from phobos, you'll have to 
provide the object reference:
signal.connect(&foo.bar, foo) instead of just signal.connect(&foo.bar)

[OT] I have to say it is a pleasure to program in D. The template 
varargs is a godsend.