New run interface

[kurtlawrence]

New interface for Repl.run().

To build a more flexible base, mortal::Screen can be employed to build a whole screen repl.

• [x] Initial implement
• [x] Editing move left and right
• [x] Backspace and delete
• [x] Multi line support
• [x] Initial completion (no prompt)
• [x] Switch . to :