FIX: Use Editline (libedit) instead of Readline (libreadline)

This fixes a GPL violation. Added bonus: command-line history on OSX.
FIX: Properly pass prompt down to Editline

When Editline is aware about the prompt, it is protected from
"backspacing" through the prompt. The prompt is also properly maintained
when recalling history.
Merge pull request #792 from earl/fix-console

Fix GPL violation and prompt protection in console