Add support for compile time reflection

[reinco]

ZSerio currently supports runtime reflection. There is no compile time reflection. With compile time reflection one can:

1. iterate over the members of a c++ struct
2. iterate over the names of the c++ fields. If a structure has compile time reflection one can define template functions that can work on any such struct. For example a comparison operator, hash function, json or yaml generated for a struct.

Compared to runtime reflecting it has the following advantages:

1. Errors in code are discovered at compile time instead of runtime.
2. Better runtime performance
3. templated function can be in a seperate header that you don't include if you do not need it. This prevents discussions on what functions a struct generated for a zserio struct must support and prevents code blot in the code emitted by the zserio compiler.