removed INFO prefix at INFO level and add colour

For the colour, I went with subtle tones, following the lead of gulp and Bau:

FATAL: red
ERROR: dark red
WARN: dark yellow
INFO: gray
DEBUG: dark gray
TRACE: dark magenta

One advantage of these is that they work better on both black and white console backgrounds since they are closer to the middle of the palette.

If we don't mind more vibrant colours we could go with:

FATAL: yellow on red background (or vice versa)
ERROR: red
WARN: yellow
INFO: cyan
DEBUG: green
TRACE: gray

These are the default colours used by the coloured console logger in NLog (with the exception of FATAL).

Or some other scheme?

Any opinions?

INFO:
![image](https://cloud.githubusercontent.com/assets/677704/3007868/dd1c81a0-dea2-11e3-8503-b9b85321350a.png)

DEBUG:
![image](https://cloud.githubusercontent.com/assets/677704/3007874/0b699f02-dea3-11e3-8bc8-e8454d584f3a.png)

ERROR:
![image](https://cloud.githubusercontent.com/assets/677704/3007876/2748c234-dea3-11e3-886a-0fb21dab3923.png)