Add a timed context manager to statsd.

[clokep]

This enables a context manager in statsd so you can easily time a set of code without saving the start time, etc. manually:

    with statsd.timed_context('user.query.time', sample_rate=0.5):
        # Do what you need to ...
        pass

    # Is equivalent to ...
    start = time.time()
    try:
        get_user(user_id)
    finally:
        statsd.timing('user.query.time', time.time() - start)

Two tests are also added for this code.

Fixes #25

Please let me know if you want anything changed, etc. I'd love to see this in the next release!

[yannmh]

Great feature @clokep, I love it. Thanks!

I think we could make statsd.timed acting as a decorator and a context manager, c.f.
http://stackoverflow.com/questions/9213600/function-acting-as-both-decorator-and-context-manager-in-python

What do you think ?

[clokep]

@yannmh Sure, seems reasonable -- I'll just need to add a __call__ method to my decorator. I'll try to get to that "soon".

[clokep]

@yannmh Please let me know if this works for you. I wasn't sure if you like to squash things or not.

[yannmh]

Thanks a lot @clokep, it works great. No need to squash, both commits lead to legit code.
Let's merge it so we can release it tomorrow with the v0.7.0 🚀 .

[clokep]

Thanks! I just realized there's a simpler way to do some of this code...same behavior, just reducing some code.

Feel free to merge percipient@f1c8db2 if you'd like.

[c-warwick]

do I need to include pass at the end of my code?