Add timeout option to client methods

[minglecm]

This change adds a backward-compatible timeout option to each client method.

Without the ability to provide a timeout, requests can hang (I think up to the global max socket timeout in Python).

See: http://docs.python-requests.org/en/master/user/quickstart/#timeouts

Alternatively, a single timeout could be provided when instantiating a Client. This approach wouldn't require changes to methods other than request. However, given the wide range of methods that the client provides, this more granular timeout may be preferred.

Also, I imagine this should be a minor version bump 1.2.1 -> 1.3.0. Let me know if you'd like me to make that change in setup.py as well.

[epels]

Hi @dentafrice, thanks for opening a pull request! Being able to set a timeout for requests does indeed seem a useful enhancement.

I do think providing the timeout to the Client's constructor as an (optional) argument is the favourable option here: that would make it consistent with how this is handled in our other clients like Node and PHP. Additionally, it makes the method calls more concise. What do you think?