Fix options, tweak colors.

- Add Javadoc to `Dispatcher.dispatch()`. Explain the logic for the
  dispatcher.
- Check for "Werror" option earlier.
- Add FATALs to "nowarn"s.
- Return 0 if the only errors are warnings, 1 if error or fatal.
- Change Severity.ERROR to CYAN. Blue was too hard to read on Windows.
- Change use of ansi colors. Now it's Color.WHITE.wrapAround("string").