Made build.xml detect OS.

Detect the OS (either Mac OS X or Linux) and use this to set the
proper path for processing such that the core libraries and the
added libraries can be found.
Reduced space between tiles.

Cut the space between tiles by half in all dimensions to get a
denser cube.
Added .DS_Store and build/ to git ignore file.
Added directory to git ignore file.

Added modes directory to git ignore file to not show Processing's
modes directory.
Added oscP5 library to repo.