allow to check OPENSENSE format conventions

[cchwala]

I have a first prototype for checking that a file conforms to the OPENSENSE WG1 data format conventions here.

This is easy to implement here. But we should do that in parallel to the discussion and decision on how to do versioning of our data format conventions.

Also see the discussion in OpenSenseAction/OS_data_format_conventions#4

[cchwala]

What will be missing in #76 is that the data formatting is checked. Once we have functions to check data format conventions, this should also be done with the example data that is downloaded via the implementation in #76.