Allow for colons in zsh completion values and descriptions, related to #162

Note that because of the startswith check escaping the completion options in the client side is not an option, as a value that includes a : for incomplete in will not pass this check.

Note that we need two levels of esacping, one for zsh, and one to preserve the escape for zsh

Tested by updating the demo.py example in the linked issue to the following:

import typer

image_desc = [
    ("alpine:latest", "latest alpine image"),
    ("alpine:hello", "fake image: for testing"),
    ("nvidia/cuda:10.0-devel-ubuntu18.04", ""),
]

def _complete(incomplete: str) -> str:
    for (image, desc) in image_desc:
        if image.startswith(incomplete):
            yield image, desc

app = typer.Typer()

@app.command()
def image(name: str = typer.Option(autocompletion=_complete)):
    typer.echo(name)

if __name__ == "__main__":
    app()

use the provided docker image/setup to test, first that the colons show as values and descriptiosn correctly

0252e3324b42# typer demo.py run --name [TAB]
alpine:hello                        -- fake image: for testing
alpine:latest                       -- latest alpine image
nvidia/cuda:10.0-devel-ubuntu18.04

and that an incomplete value with a colon generates options

0252e3324b42# typer demo.py run --name alpine:[TAB]
alpine:hello   -- fake image: for testing
alpine:latest  -- latest alpine image