Redesign obj to exe/lib mapping

Specifically:

* objso{} and libso{} target types have been renamed to objs{} and libs{}

* obje{} has been added (so now we have obje{}, obja{}, and objs{})

* obje{} is now used for building exe{}

* object file extensions have been changed to use "hierarchical extensions"
  that reflect the extension of the corresponding exe/lib target (instead of
  the -so suffix we used), specifically:

  obje{}: foo.o, (UNIX), foo.exe.o (MinGW), foo.exe.obj (Windows)
  obja{}: foo.a.o (UNIX, MinGW), foo.lib.obj (Windows)
  objs{}: foo.so.o (UNIX), foo.dylib.o (Darwin), foo.dll.o (MinGW),
          foo.dll.obj (Windows)

0 files changed, 0 insertions, 0 deletions