Test in Python 3.5 too, now that it is out

Cache page text until next edit operation

Store the results of page.text() operations in a simple cache
dict. This avoids unnecessary remote roundtrips. Cache is
cleared on each successful page.save() operation. cache
argument can be set to 'False' to disable use of the cache.

Remove unused local vars

This attribute goes back to an older design, where
the 'edit page' workflow was different: the edit() method did
part of the work of defining what text you meant to edit. In
the current workflow, text() - which replaced the deprecated
edit() - is only for retrieving text, and save() is supposed
to do all the work of editing the page.

The 'section' attribute is therefore obsolete and dangerous.

- Remove :ref:s from the headers, since they made the latex build crash
- Add logo

Remaining issue:

- Can't get headings levels right on both the html and the latex builds
  at the same time. More info in #40

While the 'backlinks' method has a 'redirect' option,
there is no such option for the 'embeddedin' method.

See 90b87566 for context

Also change link to the slightly user-friendly Phabricator (the url looks nicer without the escaped slash, too)

Removing unsued import

From client.py: time, random, sys, weakref
From sleep.py: random

Merging changes from mwclient master

Since CirrusSearch (and Lucene?) doesn't support 'title'.

Since default values are evaluated only once, mutable objects shouldn't be used.

I've no idea when this would actually be needed, but at least it should be fixed now.. It broke during the move to use the requests library.

log.warn has been deprecated

- Moving code related to waiting/sleeping/retrying into a new class for a more object oriented approach.
- Removing any reference to wait "tokens" to avoid confusion with edit tokens.
- Note: `max_retries` and `retry_timeout` are no longer available on `Site`, but can still be passed into the constructor as before.

- The method has been broken since the move to requests (wrong number of args sent to self.site.connection.get)
- Add option to stream the file to a file object

Should at least be compatible with Python 3.4 now.
Can't get Python 3.3 to work locally, but let's see with Travis.

- Factor out parse_timestamp
- Use `iterkeys`, `itervalues`, `iteritems` and `next` from six
- Use __next__ for Python 3.x and next for Python2.x