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 
What I'm worried about is changing the user's environment for other contexts. For instance: A user has been using gcc for building some other projects, they run these commands here, then gcc no longer refers to the same version of gcc and other projects could potentially break! We definitely need users to `install g++-4.7`, but instead of changing the name "gcc" to refer to this new version, we should tell CMake to specifically use g++-4.7