Return human-friendly colorized error if output device is a TTY

Otherwise, print the Twilio error string
Merge branch 'master' into tty
Merge in latest master
Update ANSI escape codes

Check that they work with Unicode. Add a background color so the message looks
OK against dark and light backgrounds. Make the color scheme slightly less
hideous.
use default background color
Merge branch 'master' into tty
PEP8
fix test
fix for py3
Merge pull request #140 from twilio/tty

Colorized output if stdout is a tty