Simplest layout by default

[evanp]

This driver got complex. I'd like the default to be much simpler. So the default layout would be:

• database
  • type1
    • id1.json
    • id2.json
  • type2
    • id3.json
    • id4.json
  • type3
    • hash:asdfasdf.json
    • id5.json

I think this works if the default hashdepth is 0; if hashing filenames is off by default; and if we only hash filenames if needed (if ID is not a legal file name).

I think this would require a major version number.