Proper stasm compilation

This branch introduces a new method for compiling STASM into a library prior to compiling OpenBR, then links against said library.  Previously, STASM source was simply included in OpenBR and compiled as OpenBR was compiled (in fact, I think STASM code was compiled twice initially - once for STASM itself and once for OpenBR).

While this branch doesn't introduce any new functionality, it significantly cleans up the install structure when installing OpenBR with STASM, and better compartmentalizes functionality.  Specifically:

* STASM headers are now installed to ```CMAKE_INSTALL_PREFIX/include/stasm```.
* STASM libraries are now installed to ```CMAKE_INSTALL_PREFIX/lib/``` (or ```CMAKE_INSTALL_PREFIX/lib/``` and ```CMAKE_INSTALL_PREFIX/bin/``` on Windows).

Also, STASM's original implementation relied on a wonky include hierarchy, where every file would include a single header that included all possible stasm headers.  I've gone through and fixed the dependencies to a more standard structure.

A notable contribution of this branch is the new implementation of FindStasm4.cmake.  I believe this structure should be used moving forward when we want to link against external code (more than a few files) that is not already compiled into libraries.