Build static and dynamic library and separate test program

This pull request implements the following:

make will build static and dynamic libraries
rearranged code into library and non-library parts
test programs are now stand-alone and will link against the library
add a prefix ft8_ to all public functions to avoid name clashes in applications that use the library - static functions were left as is
fix a couple of bugs that could lead to crashes
Added Xcode project (mainly because that's the environment I use and made refactoring easier) - feel free to delete if you find it unsuitable
probably some small cosmetic changes

kgoba / ft8_lib