* Add python typing module as build dependency

* Change output_declarations to be a NamedTuple

* Add mypy configuration files

mypy-files.txt includes a list of all files that should be typed checked
with mypy. Run mypy with `mypy @mypyfiles.txt`.

mypy.ini includes mypy options. Unfortunately this can't be merged with
mypy-files.txt.

Update .travis.yml so that one doesn't have to specify what files to
type check inside it.

* Add RuntimeError on missing `typing` module

Alerts users to the new build dependency.