Adding a test file for the BlfReader

[felixdivo]

This idea came up here, to create a BLF test file ourselves, that contains all/most of the features we support.

[felixdivo]

@christiansandberg Maybe you have the tools for that.

[christiansandberg]

Sorry, I don’t have that anymore. But maybe I could create a script that generates a file using python-can and someone else could verify that it is valid.

[felixdivo]

Seems like this was done in #734.