Add client support for Service Discovery

[caedes]

This patch provides a DiscoClientProtocol?, implementing item and information requests and acompaining unit tests.

Note there is a little overlap with the muc branch, where DiscoQuery? is defined as DiscoRequest?. I think this name is more consistent with others in the file, but the detail is not so important to me either, so it could be named back to DiscoRequest?.

Other considerations... about the request functions, i wasn't very sure if i should return items, the iq, or even filtered items as the pubsub.items() does. I thought filtering them can be counter productive, but found the convenience of returning the items compelling enough as it abstracts away some complexity, so i took this middle alternative. I'm also happy with a different approach.

[caedes]

DiscoClientProtocol? implementation and unit tests.

[tofu]

(In [137]) Creating a branch to apply and review patch. re #28

[tofu]

(In [138]) adding patch from caedes re #28

[tofu]

This patch looks ok. The tests pass. I think the tests need comments. I also think the tests need to test the returned items.

I also think the items returned should be a list of wokkel.disco.DiscoItems? instead of a list of domish.Elements

[tofu]

I retract my statment about the return values, I think domish.Element is fine, since there really is not much more to a DiscoItem? and it very simple. I do not think we should filter.

I also think that the muc branch can be changed to work these changes in. I will leave it for ralph to decide to merge this or not.

[ralphm]

(In [143]) Branching to 'disco-client-28-2'

[ralphm]

I branched forward after closing #7 and am going to work on this before merging.

Besides more docstrings and better tests, I agree with tofu's original statement, We should have generic objects for items, features and entities and maybe a container for info to hold features, entities and ​Service Discovery Extensions (XEP-0128) forms. Each of these would provide toElement and fromElement methods to render to an Element and parse from an Element respectively. I started this pattern for Data Forms as part of #13 and made objects for publish-subscribe events, too.

[ralphm]

(In [145]) Implement proper objects to hold service discovery information and items.

This changes the existing objects that derived from domish.Element, to objects in their own right that can be created from an Element using fromElement or rendered to an Element with toElement`.

Re #28.

[ralphm]

I think my work for providing nice container objects for parsing from Elements and rendering to Elements is done. I modified to the client code to use it. For example requestInfo returns a DiscoInfo object with features, identities and extensions attributes for easy access to the parsed response.

Please review.

[tofu]

I do not see any reason not to merge this. I will merge it.

[tofu]

(In [157]) merge source:/branches/disco-client-28-2 fixes #28