Smart colorization, improved header and more

Lots of improvements. Most notable:

-   Now there is no color if output is not to a tty.

-   Previous header was:

        [1.9.3-p194]: <command>
        *********************************************

    It took two lines and displayed the command unnecessarily for each Ruby.
    Now the header is:

        ===[1.9.3-p194]==============================

Fixes #6