Adjusted CMakeLists and added options to build as a library
Added symbols to be Exported, moved ctors to cpp files to avoid exporting getFactoryFunctions
Added option to build with static GLEW defaults to not, fixed formatting in FindGLFW3
Make sharedlib + exe the defaults
Adjusted travis.yml glfw settings
Adjusted output names (libSigma instead of liblibSigma)
Made the output directories for library and executable the same
Changed output names, Sigma.dll/.lib Sigma_static.lib on Windows, libSigma.so/.a on Linux
Merge pull request #133 from Meisaka/libSigma

Make Sigma a library, would close #85