don't let artistic style write .orig files

- only format code after compile
- format all sources files
validate src_files variable in compile()
move important variables up front
src_files is an array
allow running clang in verbose mode
allow passing a build style (debug by default)

and on gxx like compilers, set the debug flag on debug builds.
append sources for runtime to the build

the runtime source files are stored in a common directory:
  runtime
and in a directory for each OS for platform dependent files:
  runtime/Darwin
start writing darwin runtime (GLUT version)
rearranged source code more logically, hook up to api entry point
implement render_next_gl
implement microseconds clock on Darwin
use clock to show changing background
Merge branch 'F-RuntimeOnDarwin'

Starting runtime implementation:
- display a window with GLUT
- monotonic microseconds clock

* F-RuntimeOnDarwin:
  use clock to show changing background
  implement microseconds clock on Darwin
  implement render_next_gl
  rearranged source code more logically, hook up to api entry point
  start writing darwin runtime (GLUT version)
  append sources for runtime to the build
  allow passing a build style (debug by default)
  allow running clang in verbose mode
  src_files is an array
  move important variables up front
  validate src_files variable in compile()
  don't let artistic style write .orig files