- Added initial implementations for terms and values
- Error messages converted to pretty printer
- Colorization for error messages
- Color and console width option both as command line and repl command
I don't know how complete this is, but it certainly detects some of the
most obvious cases which are most likely to be bugs.
While I'm at it, this is as good a time as any to add a general way of
reporting warnings, similar to the way of reporting errors.
