Add PEP 484 -- Type Hints #368

Python supports type hints to improve static analysis:
https://www.python.org/dev/peps/pep-0484/
This helps to identify cases, were wrong types are passed into functions et al by using type checkers likehttp://mypy-lang.org/ or https://github.com/google/pytype/.

python-ldap does not yet seem to contain those annotations nor am I aware of any project doing that.
Those annotation can either we added directly in the library like

def func(arg: str, val: int = 0) -> Tuple[int, str]

since Python 3.5 or in a Python-2 backward compatible way as

def func(arg, val=0): # type: (str, int) -> Tuple[int, str]

As an alternative the annotations can be put into so-called "stub files" names "*.pyi", which are collected by https://github.com/python/typeshed, but inline annotations are preferred as they are easier to keep in sync.

I started working on that, but other projects have preempted that
effort. My current work is at
univention/typeshed@8fc5f79,
but it not much more then generating the stubs using stubgen.
If someone wants to join that effort that is much appreciated.

This was proposed to the Mailing List.
@tiran proposed to start the work only after the Python 2 legacy code is removed:

we are planning to drop support for Python 3.5 and earlier in the next
version of python-ldap. This would make it simpler to add signatures for
type hints directly to the code base. Patches are welcome, but please
wait until we have finalized Python 2 cleanup in master.