Resolve Loader memory leak from rP2232.

Use C++11 featured shared_ptr to avoid conditional deletion in multiple locations.
Drops C compatibility(?) of Loader.h.

Differential Revision: https://code.wildfiregames.com/D2331
Tested on: clang 8.0.1., Jenkins
Comments on IRC #wfg 2005-05-07
Refs rP2027, rP2032, rP2038.