large output makes Emacs freeze, lp:1253907

fixed

`py-fast-process', new commands suitable for large output

Repeated calculations by comint-mode are considered
responsible - bug only showed up in this special case.

Solution uses `process-send-string'; comes with a
couple of new commands prefixed "py-fast-"

If new option `py-fast-process-p' is `t', result arrives in
py-output-buffer, which is not in comint-mode

####

Rewrite - as slicing in new function demanded several changes

  Python code now might be processed by an
  - interactive Python shell (DEFAULT)
  - non-interactive Python (`py-fast-process-p', if large output)

  Both processes might run in
  - session, i.e. start from possible previous state (DEFAULT)
  - dedicated, run in separate process
Doku updated
Provide menu for fast processing commands, lp:1253907