Adding interface for setting kernel filter

[LehmRob]

Adding a function for the Bus object which makes it possible to activate a kernel side filtering for CAN frames. The function takes an array of unix.CanFilter objects.

The kernel side filtering reduces the load for the application if only a subset of received CAN frames are interesting.

[LehmRob]

Any feedback? Please tell me if there is something wrong with the pull request.

[brutella]

Thanks for the pull request.

Not sure why you removed parts of the readme.
You changed the module name to github.com/sitec-systems/can – but it should actually be github.com/brutella/can.

[LehmRob]

Oh sorry for that. That's my first pull request and I didn't know that further commits are landing here as well. I reverted the changes on the README. Again sorry for that.