drops whitespace
refactors hash into constant
fixes naming scheme

cast is more explicit and more active voice.
documents customized type casting options
bumps version number
uses strings as prefix default - not nil

gets rid of ternary, and is more explicit about what is expected
uses introduced variable

prefer the cast for types not found in the CASTS hash, and fall back to
trying to use the same type across dbs.
removes unnecessary variable

incremental_load_action#prefix is hardcoded to return an empty string,
so this is never actually used. that's cool.