VehicleDatabaseFormat

TODO: the database format needs to be explained here. For now, the best current description is in the comments at the top of the [DatabaseToyotaNHW11] xml file. It's an evolving format at this stage, already know some things that should change.

Reported issues

#1
extend database format to describe more than PIDs

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a note: the most similar existing format I know of is the logger.xml format that seems to be used by the projects RomRaider, EcuFlash, and something called Enginuity (no idea if that's related to the commercial AutoEnginuity product). An example of the file format is here and its DTD here.

It allows a parameter element to have multiple conversion elements to different units, with more general arithmetic possible (it has expression strings to be parsed rather than fixed mul, div, and add) and it labels units, but not in UCUM syntax. If we run into parameters that need calculations that can't be simplified to mul, div, and add, we could have to generalize the expression syntax, but better not to do that unless it becomes necessary, since we want to keep the ability to export tables for ScanGauges, etc., that only have the simple calculations.

The logger format isn't designed for subsuming other formats and being able to re-export them, so it isn't ideal as a central repository form where databases can be hashed out. But it shouldn't be too hard to convert from it to our format, and re-export it when wanted, as with any other format.

I don't know how many vehicle databases might be available in that format. The RomRaider site seems Subaru-specific, and the EcuFlash site mentions only Subaru and Mitsubishi, but that doesn't mean databases in that format for other vehicles might not be posted on forums somewhere.