cmd/geth, jsre: restore command line editing on windows

PR #856 broke command line editing by wrapping stdout with a filter that
interprets ANSI escape sequences to fix colored printing on windows.
Implement the printer in Go instead so it can do its own
platform-dependent coloring.

As a nice side effect, the JS console is now noticeably more responsive
when printing results.

Fixes #1608
Fixes #1612