Smart colorization, improved header and more

[mislav]

Lots of improvements. Most notable:

• Now there is no color if output is not to a tty.

• Previous header was:

  *********************************************

  It took two lines and displayed the command unnecessarily for each Ruby. Now the header is:

  ===[1.9.3-p194]==============================

Fixes #6

[avsej]

:+1: