Directory cleanup and Makefile for code generation

I have moved the content files to their own directory and have made the directory structure easier for cross-platform development by splitting up the source into sub-directories.

In order to build the project, change to the source/<platform> directory, for now only Linux is supported:
/ $ cd source/linux

Next, issue make.  With an optional debug (default), release, or profile build target:
/source/linux $ make

There should be a file called legend-of-pandoraD_<GCC version> in bin/linux/x86/64 along with the content files copied over from the content directory.

Run the file via:
/bin/linux/x86/64 $ ./legend-of-pandoraD_<GCC version>