Setter methods for subreddit settings

[pl00h]

It would be useful to have the ability to set subreddit settings (and the type and other info that we can currently get but not set).

[Yay295]

I believe this is somewhat related to #31.

[fsvreddit]

@pl00h I don't think this is a duplicate, #31 isn't related to the ability to set subreddit settings from code