Bugfix in output_screen_diff: always clear last_char on reset. + some small improvements.
Bugfix in output_screen_diff: always clear last_char on reset. + some small improvements.

jaseg/python-prompt-toolkit,ddalex/python-prompt-toolkit,amjith/python-prompt-toolkit,ALSchwalm/python-prompt-toolkit,melund/python-prompt-toolkit,jonathanslenders/python-prompt-toolkit,niklasf/python-prompt-toolkit