Missing dependencies when installing from pypi

[Looby72]

Currently the download from pypi is missing some dependencies that make it impossible to build the python module.

When trying to use pip install pysame the following error occurs:

CMake Error at CMakeLists.txt:77 (add_subdirectory):
        add_subdirectory given source "third_party/gflags" which is not an existing
        directory.

      
      ---Building benchmarks 
      ---Done building benchmarks
      CMake Error at CMakeLists.txt:111 (add_subdirectory):
        add_subdirectory given source "third_party/pybind11" which is not an
        existing directory.

      
      CMake Error at CMakeLists.txt:112 (pybind11_add_module):
        Unknown CMake command "pybind11_add_module".

In detail the submodules included in the /third_party directory are missing in the source tree downloaded from pypi.