v0.3.1

Minor Release with updates to CMake installation process.

• Headers are now installed in nested fashion with a parent-level header representing each module. For example:
  • Files in a module directory such as the ml/ directory (linreg.hpp, logreg.hpp, mlp_network.hpp, etc.) will make up that modules header file(ml.hpp).
• Will include googletest workflow into CMake installation
  • Build library -> Test library -> Install library