Add more options that pass through to `isort`

[asottile]

At yelp we'd probably like to use a couple of the other flags that are available.

[dinoshauer]

Any specific flags in mind?

[asottile]

From an intial glance at the code I think force_single_line at least is something yelp is interested in

[dinoshauer]

Actually, isort is configurable with a config file .isort.cfg which the commit hook supports. An example for you might be as following

[settings]
force_single_line=True

I will update the readme and possibly deprecate --show-diff

[asottile]

Ahh yeah the config file is a much better option :)