Fixes a bug with slots in PyPy.

PyPy slots are not instances of types.MemberDescriptorType. PyPy's
types.MemberDescriptorType is the as types.GetSetDescriptorType but neither is
the type of slots. So let's keep using MemberDescriptorType for identifying
slots.
Improves the test for beta releases
Removes a bunch of commented code
Removes mdeco
Jumps to version 1.3.0 and fixes HISTORY
Master should not have a dev tag
Fixes index organization in documentation
Jumps to 1.3.0.1
Makes :meth:`xoutil.collections.StackedDict.push` return the level
Makes StackedDict an SmartDict. Also moves SmartDict to collections.
Removes old/uncompleted code.
Removes the deprecated return_tuple argument of first_n
Fixes versionadded directive
Removes unneeded examples. The docs are clear enough
Removes deprecated first, and get_first. Deprecates obtain. Introduces first_non_null.
Deprecated get_flatten_list, izip and imap
Changes the notion of collection in first_n
Adds the notion of collection for `fill` argument in function `slides`. Adds a whole bunch of tests for iterators
Makes the doc module xoutil.data to be generated automatically
Updates the documentation of xoutil.iterators