support more shells (fish / csh / bash / powershell)

I’m using fish and looks pipenv works fine without shell command:

❰/private/tmp/asd❱✔≻ pipenv shell
Spawning virtualenv shell (/usr/local/bin/fish).
Unsupported use of '||'. In fish, please use 'COMMAND; or COMMAND'.
/private/tmp/asd/.venv/bin/activate (line 23):     if [ -n "${BASH-}" ] || [ -n "${ZSH_VERSION-}" ] ; then
                                                                         ^
from sourcing file /private/tmp/asd/.venv/bin/activate
	called on line 194 of file /usr/local/Cellar/fish/2.4.0/share/fish/config.fish

in function '.'
	called on standard input

source: Error while reading file '/private/tmp/asd/.venv/bin/activate'

Seems it is trying to active the virtualenv with bin/active, but virtualenv also support fish via bin/active.fish, i think we can source it while detected current shell is fish.

And also, i think pipenv dose not support csh / cmd.exe now…

[kennethreitz]

going to drop windows support for now.

[jessebraham]

@uranusjr It is possible to detect the difference between Powershell and Command Prompt, for example using the psutil module:

import psutil
import sys

if sys.platform() == 'win32':
    me = psutil.Process()
    parent = psutil.Process(me.ppid())

    # Prints 'powershell.exe' or 'cmd.exe'
    print(parent.name())

However as you mentioned, pexpect.spawn is not supported on Windows, and there are no plans for it ever to be.