Convert to ANSI escape code colored diff output as default in terminals

[chrissimpkins]

Closes #52

This PR includes the following changes:

• ANSI escape code colored diff output is the new default in terminal environments (previous default was no color). The previous uncolored default is maintained when stdout is piped to non-tty like devices.
• a new --nocolor option is added to toggle color off in terminal environments
• the -c / --color option is kept to both prevent breakage in existing workflows and force escape codes in non-terminal env's
• reorganizes the --help menu option list with some semblance of order

I addressed a separate issue in this PR:

• The message to users when no OT table diff was identified has been changed from "There is no difference between the files" to "There is no difference in the tested OpenType tables".

These changes will be released in v3.0.0