experimental no-GUI version of tracker

This version splits out all the OpenGL stuff leaving a pure command-line
tracker.
main_nogui: remove unused code
main_nogui: move callbacks under main()

It's more readable to have code-flow weakly follow layout.
main_nogui: separate callback functions with blank lines
main_nogui: indentation fixes
main: remove logging

main_nogui can now perform logging.
main_nogui: clean up before exiting
main_nogui: convert to God's own line-endings

(i.e. Unix style)
main_nogui: make sure to include cstdlib for EXIT_SUCCESS
main_nogui: refactor context initialisation to separate functions
main_nogui: refactor depth generator node creation

Move creation to separate function.
main_nogui: fix typo in "declarations"
README: add note on non-gui application
add lean-mean option parser for C++
nogui: add a simple command-line interface

Most importantly, running the command with no arguments now prints out a
usage summary.
main_nogui: specify log-file output file prefix
main_nogui: add "--duration" option

Allow specification of how long main loop should run.
Merge pull request #10 from rjw57/no-gui

Re-factor into GUI and non-gui versions