Experimental macros for mocking functions with inferred arity

Not having to state the number of arguments to a function when defining a mock has been on the wish list from the very beginning of Trompeloeil, and is an open issue since 2017!

There is now experimental support for new mocking macros that, finally, does away with that.

MAKE_MOCK(name, signature) and MAKE_CONST_MOCK(name, signature). The caveat is that the signature must be written in trailing return type syntax.

struct S
{
    MAKE_MOCK(func, (int, double)->bool);
};        

Please try it out and report your findings.

Also, a matter of taste; would it be better if the syntax required the auto keyword? MAKE_MOCK(func, auto (int, double)->bool)?

The functionality is available on branch trailing_return_type