Bundle documentation improvement

Silenced all the doxygen warnings coming from Bundle by documenting the
various undocumented methods, operators, and parameters.

Got rid of the init_list typedef it's only used 4 times: twice each in
Bundle.hpp and Bundle.cpp.
Documented WrappedPositional<T>

Previously WrappedPositionalBase was carrying all the documentation,
but much of it really belongs in WrappedPositional.

Added WrappedPositional<T> constructor documentation.