Closes #125

- Most importantly, the 'protectedpage' error was missing in the list.
- Improve string representation of the error.

- When `Site.force_login` is True we can send `assert=true`
  with `edit` actions to have the api reject our edits if
  we got logged out for some reason.
- Adding a new exception `AssertUserFailedError` as a subclass
  of `LoginError`.

Closes #126

New implementation of #126

- move stuff out of while loop that doesn't need to be there
- make url in one step

Use MANIFEST.in to specify that LICENSE.md should be included in the
source distribution. Fixes #140

otherwise the logo gets awkwardly separated from the title

PR #136 fixes #88

To avoid stuff like #135 from happening, make it more transparent what's
going on in `List.__next__` by
- replacing the check for `full=True` with
  `isinstance(self, GeneratorList)`
- replacing the recursive call to `List.__next__` with
  `item = six.next(self._iter)`. This means one line of code is
  duplicated, but I think it's pays of in term of readability.

Putting back an explicit reference to `List` to avoid
`GeneratorList.__next__` being called.

- Remove `Page.get_expanded()`
- Postpone removal of `Page.edit()` since it's a more popular method.

per #130

- https is standard now, so no need to explicitly declare that
- wrap lines around 90 chars
- minor rewriting

to adher to 52b9d8b8

A lot of other line length Modifications

For determining the version, I created a staticmethod (because this does
not really depend on the state of the instance) which makes things more
readable – `self.version = self.version_tuple_from_generator()` is
self-explaining and shortens the amount of code to comprehend in the
`site_init` method.

Lines > 90 chars have ben wrapped appropriately (except for a few cases
where readability would have decreased)

For membership testing against a container of multiple values, mostly
use `sets`!  Tuples are technically working, but semantically not the
right choice.  Tuples have structural meaning and are heterogeneous,
while sets concern membership and uniqueness, being the correct tool.

This is a similiar reasoning as in
http://stackoverflow.com/a/626871/2443886 concerning lists vs. tuples.

I did this kind of on personal interest, since my emacs (using flake8)
marks every violation (meaning: line >79 chars) red, which is pretty
annoying.

I personally think 90 is a realistic guideline.

Since `next` is just there for compatability reasons, it is more
reusable be completely transparent, i.e. Passing every
[keyword]argument.

Now, we don't need to re-define it in the child class with a different
signature.