Reformat
Less spew, more documentation
Add more PowerV3 status values

Part of #77

Make init_value attributes optional for parameters and signals. This is
not spec-pure but it cleans up the node file.
Fix #78 by correcting the size of the Board::kConfigMagic write

Replace some magic numbers with constants from lin_defs, and add API to
Board to check for forced bootloader entry.

Remove stale PowerV1 references.

Entangled with some changes to PowerV3 status reporting related to #77.
Change some PowerV3 status names.