* refactor(storage): move unused code to repo that needs it
Turns out that a bunch of code is only needed in IDPE. This change
removes that code, and another PR adds it to IDPE.
* refactor(storage): export KeyMerger
* refactor(storage): export NilSortHi and NilSortLo
* refactor(storage): move StringIterator & friends to IDPE
* refactor(storage): unexport a few test helper funcs
A standard Makefile is used now in all subdirs that run go generate.
Make will only generate the file if its source files changed.
The checkgenerate target runs clean to ensure all targets a generated
fresh.