Shell integration improvements and cleanups

Shell integration improvements and cleanups

Removed functions python-shell-clear-latest-output and
python-shell-send-and-clear-output in favor of
python-shell-send-string-no-output.

Also python-shell-send-string now supports multiline string statements
so you won't have to worry calling python-shell-send-file again.

All this changes should make integrations with other Python shells
than standard more robust.