Add support for output of ANSI-colored text

[n1tehawk]

This is eye-candy based on the existing "text" class, augmented by ANSI control sequences for different colors.

To use it, request "color" output, e.g.:
./run_functional_tests.lua -v --output color

[coveralls]

Coverage increased (+0.007%) to 99.831% when pulling 63ad634 on n1tehawk:20161118_ansicolors into d1a9ddc on bluebird75:master.

[n1tehawk]

Will rebase onto current master...

[coveralls]

Coverage increased (+0.006%) to 99.844% when pulling 32ac773 on n1tehawk:20161118_ansicolors into 41927da on bluebird75:master.

[coveralls]

Coverage increased (+0.006%) to 99.844% when pulling afa3e17 on n1tehawk:20161118_ansicolors into 41927da on bluebird75:master.

[bluebird75]

Initially, I was thinking about a command line option --color to deal with color. However, I see that busted also used an outputter approach to deal with the color thing, so why not...

However, the text output itself should be identical with and without colors. Internally, the best way to go is to make this an option of the general text outputting class.

I did not check your branch under windows yet, but as far as I know, unix color codes don't work in the default windows console.

[Googling a bit on the topic]

So, on windows 10, ansi color codes work out of the box. On previous versions of windows, using program such as ansicon can make them work but I find the approach tedious.

So, as first step, let's just enable colors on unix. We will improve later on Windows support.

[n1tehawk]

I selected the "outputter" class as a natural approach at first, but I do agree that we're duplicating code from the text output. And I assume that we don't expect to require any other output that would be 'colored'?

Re-uniting the code should be straightforward enough. We could start with a COLOR table that initially holds empty strings, and only set those (to the needed control sequences) when --color is encountered. If older Windows (Win32 console) needs special treatment, we could introduce a different option (--wincolor?) to adjust the control strings. The text outputter would just always concatenate the COLOR strings to its output; in the case of "plain" text those would simply be empty.

[coveralls]

Coverage increased (+0.001%) to 99.839% when pulling 593a3e3 on n1tehawk:20161118_ansicolors into d2f1ffa on bluebird75:master.

[n1tehawk]

Fixed typo in commit message, rebased to current master

[coveralls]

Coverage increased (+0.001%) to 99.839% when pulling b7d7722 on n1tehawk:20161118_ansicolors into d2f1ffa on bluebird75:master.

[coveralls]

Coverage increased (+0.002%) to 99.71% when pulling c6aa528 on n1tehawk:20161118_ansicolors into 4345dbd on bluebird75:master.