Color REPL under -Dscala.color

We already use -Dscala.color when using -Ytyper-debug

This tries to reuse the colors chosen from the debug flag:

* Bold blue for vals (e.g. "res0")
* Bold green for types (e.g. "Int")
* Magenta for the shell prompt (e.g. "scala>")
Automatically enable color REPL if JLine says so
Merge pull request #63 from puffnfresh/feature/color-repl-auto

Color REPL