use a validation library

[asmodehn]

To validate our data, we currently use custom code.
We should use an existing library when possible.
Ex : https://github.com/alecthomas/voluptuous

[asmodehn]

We could also rely on python3 types, and corresponding tools like mypy

[asmodehn]

There is also https://github.com/maximkulkin/lollipop and https://github.com/maximkulkin/lollipop-hypothesis
=> ros-hypothesis anyone ?

[asmodehn]

maybe we also could have that at a higher level...
The plan so far is to have pyros-msgs expose the same API as ROS but with improvements, and pyros-schemas / marshmallow is probably python specific, since we have an interface of ROS messages as dictionaries...