Store assignments under next start hex instead of end hex.
Store assignments under next start hex instead of end hex.

Storing assignments under the first number *inside* the range and the
first number *outside* the assignment allows us to compare assignments to
neighboring assignments later on.

This change requires moving to new database cache version 0.0.3.

d1b/blockfinder,Starefossen/docker-blockfinder,ioerror/blockfinder,ioerror/blockfinder,d1b/blockfinder,Starefossen/docker-blockfinder