Feat: `repr()` uses class name and Travis-CI fixes

[alastairmccormack]

I regularly use AttrDict to quickly convert JSON objects into what looks like native objects.

When getting the repr, it's nicer to see the subclassed name rather than AttrDict.

E.g.

>>> class MySubClass(AttrDict):
>>>    pass

>>> msc = AttrDict({})
>>> print(msc)
'MySubClass({})'

[coveralls]

Coverage remained the same at 100.0% when pulling a7421d913542cf074d0d094ea844915e61a3f1e2 on use-sparingly:feature/repr_subclass_name into 9f672997bf576008e2990864bb9c085b3083896a on bcj:master.

[coveralls]

Coverage remained the same at 100.0% when pulling f6b6fdeb68cca90b776266bad8cd9711c003f3cc on use-sparingly:feature/repr_subclass_name into 9f672997bf576008e2990864bb9c085b3083896a on bcj:master.

[alastairmccormack]

To make the Travis CI build pass I've had to drop Py 3.2 and 2.6 tests. It seems that many libraries are dropping support which is causing pip install to fail on these versions.