Support for C methods

[edwardalee]

I've added support for methods in C because I need this to implement LET.
The invocation of a method in target code is a bit awkward.
You have to do this:

    self->my_method(self, my_arguments);

But with this design, method names need not be unique across reactors.

[Soroosh129]

There is an alternative way to do this using #define and #undef within the body of reactions.

foo_reaction_function_1(...) {
    #define my_method(var1, var2) foo_my_method(self, var1, var2)

    #undef my_method
}

This would make the syntax for accessing methods slightly different though from the syntax for accessing state variables.

[edwardalee]

Great idea! I will do this.

[lhstrh]

I personally don't find using the self struct to find a method all that awkward. In fact, that's were I would look for them given that's where state variables live...

[Soroosh129]

Looks great!