Add macros to support overloaded signal names

[hs-apotell]

Copperspice has the macros that allows overloaded functions to be used as signals but cs_signal is missing those functions.

Following code throws compile error in cs_signal but works as expected (with alternative macros) in copperspice.

SIGNAL_1(void added(ClassA *a)
SIGNAL_2(added, a)

SIGNAL_1(void added(ClassB *b)
SIGNAL_2(added, b)

There are some discussions (#2) that talk about supporting overloaded signals but I can't seem to find any examples of how to use it.