explicit int sizes for c-ffi

[iglennrogers]

In re #57. It might be an idea to have explicit int sizes when defining an interface.

At the moment, you have <c-int>, <c-short> et al, but libraries usually define an "int16", "int32", "uint16" etc. For clarity and ease, it would be nice to have direct analogues, <c-int32>, <c-int16> etc

I'm assuming that it's just a case of something like define constant <c-int16> = <c-short>

[hannesm]

You've seen http://opendylan.org/documentation/library-reference/c-ffi/index.html#fundamental-numeric-type-designator-classes ? but I agree, we should have a set of convenience constants for those datatypes. Happy to accept a pull request.

[hannesm]

I especially meant the table http://opendylan.org/documentation/library-reference/c-ffi/index.html#the-integer-designator-classes-and-their-mappings