Remove deprecated signal attribute from example.
Let VI handle passthrough by setting passthrough attr on CanBus.

See openxc/vi-firmware#222.
Use a multiplier to generate spaces for indentation.
Add an explicit argument for the output formatter.
Add fabric tasks for coverage and diffcover.
Abstract streamed, formatted vehicle messages out from data source.
Support (de)serializing all message types as protobufs.
Handle kwargs in all sources and handle format in parent class.
Use whatever the current format is for control commands.
Merge branch 'next' into built-in-passthrough

Conflicts:
	openxc/controllers/base.py
	openxc/generator/structures.py
	tests/test_generator.py
Set formatters for each interface in addition to streamer.
Add a command to openxc-control to set passthrough status of bus.
Make sure VI commands include delimiter.
Refactor the CLI for the passthrough command.