Adding core base files for raspberry Pi

- libtess2 is linked as a share library
- in the documentation I put how to switch the cmake version to avoid compiling cmake-3 on the rpi
- Pan gesture with mouse + Pan and Zoom with keyboard 
Ok, this will work until the user logs out and the environment variables are reset haha. What I meant is to put a line in the CMake file like `SET(CMAKE_CXX_COMPILER "g++-4.7")`. Can you try that and tell me if it works?