Split readline into submodules.
Add a Completion readline mix-in.
Add Pygments highlighting mix-in to readline.
Remove an invalid line from readline's README.
Rename completion_word to completion_regex
Change the description of readline.History.
Fix complete_event.
Make default `display_completions` display stuff in columns.

This mirrors GNU readline's behavior.
Add completion and Pygments-based highlighting to the REPL.