This pull requests contains a couple requested changes to the CMake files:
Allow the use of a previously-installed bamtools that's in another location, rather than requiring the user to download & install bamtools in the eXpress directory. I have access to a compute cluster where bamtools is installed and available via environment modules, and this method allows the user to specify the location of libbamtools.a via, e.g., the CMAKE_LIBRARY_PATH environment variable.
At least on CentOS 6.7, librt and libpthread are needed when linking the express executable. It should hurt to include these for other *nix variants, as both libraries are specified by POSIX.
This pull requests contains a couple requested changes to the CMake files: