Improve client's API

[flaper87]

The idea is to implement an API along the lines of python-requests.

[chris-morgan]

Note that this should be an addition, sitting on top of what is currently there (though that too will doubtless be changed around quite a bit).

I'm not certain where things like redirect handling belong; a couple of designs for that that occur to me are:

• Add functions which take a response and advise on what should be done about it with an enum (this is not necessarily incompatible with other approaches);
• Add another layer which takes care of these things;
• Put this into the current client layer with flags to disable them;
• Have this solely in the "friendly" layer.

[flaper87]

I agree.

The plan is to add a separate module, which defines the API that will sit on top of the current implementation. It'll be implemented as a nice abstraction of the lower level parts of the client.

As for now, I think this should be implemented as plain functions defined within the api.rs module. Later on, a session trait could be added, synchronous support - I'm not sure whether this belongs here - and support for other things.

I'll start working on a first example and that we can brainstorm on.

[flaper87]

I won't make any pull request until it's done. I mentioned the issue in the commit for the sake of the discussion happening here.

[flaper87]

@chris-morgan ping?

[chris-morgan]

(See #23 (comment).)