Add extra DTCs for Volvo 850 & S/C/V70 as well as parser for generating them

[brendandburns]

This is a replacement for https://github.com/fenugrec/freediag/pull/95

Consider it a rough draft to see if it is in the right ballpark. It depends on the refactors in #98

Open questions:

• Do we want to compile both lists in so that users can select at runtime?
• Previously there was a desire to split into descriptions and tips, any ideas about how to do this programatically?
• Should we include the original source files into the repo? I'm not sure about the licensing/OSS implications of that.

Anyway, please take a quick look to see if it is reasonable before we move onto more detailed review.

cc @aaeegg