rewrite to use json for storage

instead of sqlite.

e4af001 updated readme
bb327d3 extensive rewrite to use json for storage:
e4856f6 more testing
3578c80 bumped version in Cargo.toml
87bf08a expanded testing
967ac7e travis using single-threaded testing
ec59c5f make test is now single-threaded
2cb85a4 testing create/delete
8d0f0b4 clarified upgrade process and note section