C++ migration: Type correctness

[davidgraeff]

Wakaama does a lot of casting. Which is a common C pattern for allowing some kind of generic code. The code does compile with a lot of warnings if -pedantic is enabled and does not compile at all if -ansi is used.

C++ templates will allow a much greater type consistency and type correctness. It is safe to assume that the C++ compiler will create smaller/faster binaries if no type erasure takes place all the time.