Use an instance of whatever the old interpreter was
don't hardcode prompts
factor out checking if buffer could be complete and is valid
import completion uses less local functions (more testable!)
split up process_event
remove unused property
all update_completion calls implicit on set current line / cursor
cleaned up process_event more
improve imports
format init of Repl more nicely
Merge branch 'innocuous-changes-for-monkeypatching' into process-event-refactor

Conflicts:
	bpython/curtsiesfrontend/repl.py
Merge branch 'process-event-refactor'