Expand functionality of wrapper generator

[x] Add generation of C and R wrappers for functions which return their result via return
- [x] C wrapper should be a function which takes and returns SEXP
- [x] R wrapper should call the C wrapper via .Call/.External
[x] Add generation of C wrappers for functions which return their result via parameters
- They need to conform to the specific format required by .C (all pointers, limited to specific types)
[x] Add registration of exported functions in C so that R can find them (reading NAMESPACE file)
[x] Add support for namespaces (read a generic NAMESPACE file and create an R-specific one)

libamtrack / ReGenerator