Implemented chmod command.  Github issue 35

I have attempted to mimic the behavior of POSIX chmod as much as possible.  I used the following resources as references and documented any deviations from the POSIX standard.

http://www.unix.com/tips-tutorials/19060-unix-file-permissions.html  (used as a spec for parsing symbolic modes like u+x).
http://www.kernel.org/doc/man-pages/online/pages/man2/chmod.2.html  (documented bit positions)
http://linux.die.net/man/1/chmod  (functionality and command-line options)

I have included appropriate unit tests and run the code through jshint.