py-fast-process use `py-fast-output-buffer'

Don't mix up with py-output-buffer known from v5 series, which
defaults to "*Python Output*"
`py-shell-complete' docstring, minor fix
`py-shell-complete': close any buffer "*Python Completions*" at start
`py-shell-complete': keep current buffer
New variable `py-result', default nil.

Internally used. May store result from Python process.
New command `py-fast-send-string'

Evaluate STRING in Python process which is not in comint-mode.
Useful for large output

`py--fast-send-string-intern' reconsidered
py-shell-input-prompt-1-regexp, py-shell-input-prompt-2-regexp

new default
These prompts sometimes appear in line, doesn't make sense to
require beginning of line