Separate the source code into separate files.

See http://stackoverflow.com/a/5128719/2578205
and
https://sites.google.com/site/michaelsafyan/software-engineering/how-to-write-a-makefile
See #8. Add colours and change welcome message text colour
See #16. Add support for `cd` and backslash escaping.

Also add current working directory and username to prompt.
See #9, #10. Add Readline support, with history and auto-complete.
Attempt to fix building on Travis CI.
Remove ncurses from dependency libraries