Adds get_sticky function to Subreddit object

[diceroll123]

My attempt at fixing my own issue, issue #402.

Unsure how to go about the 404 though, since this is new for praw. I figured since trying to view /r/lounge as a non-gilded user gives a 403 that I'd leave the 404 here for someone with more input on praw to decide.

[coveralls]

Coverage decreased (-0.14%) to 71.42% when pulling 7c2ff0a on diceroll123:master into 50afdc6 on praw-dev:master.

[bboe]

This PR looks awesome!. A few things:

• Per All exceptions should be in the PRAW namespace #378, all errors should be in PRAW's namespace. When a stickied post doesn't exist it should raise APIException (https://github.com/praw-dev/praw/blob/master/praw/errors.py#L238)
• At the very least one test that asserts the raise of APIException, and one to assert a subreddit object is returned would be perfect

It would be perfect if you could make those changes, but if you think you may not get around to them please let me know. Thanks for the contribution!

[diceroll123]

Thanks!

Also, while I'm sure I could hack together a way to do what you ask, I feel a little weary since I have no previous examples to follow the "style" of going about this. There aren't really any raised APIExceptions to learn off of for this isolated 404 (error messages and such...), so I'll leave this to someone who'd set a better standard. 👍

Though I'm glad I've given a slight nudge in the right direction for now. :)

[bboe]

@diceroll123 no worries. I'll work with what you have here. Thanks again!

[bboe]

Merged as 7f8f77d with additions and modifications in: 7a2ec7d

Thanks for the contribution!