Upgrade footprint generators to v8 format

This is a first draft of the v8 format upgrade:

• First, redo the s-expr serialisation:
  • auto-format (no manual line breaks now)
  • tabs for indents
  • distinguish between s-expr "symbols"/"keywords" (never quoted) and "strings" (always quoted in the KiCad formats, though not in Lisp-y s-exprs)

I have also upgraded the format of the unit test serialised strings. I haven't changed the tests much, but I did remove some superfluous descriptions, tags, and text items that are now properties as these are tested explicitly in SimpleFootprintTests and including them ion tests like the exposed pad tests is pointless and noisy.