* wip based on early draft. todo benchmarking

* fixup eraser, assume keys are unique

* fix cursor copy, test removal at random

* small benchmark via permutations. todo lambdas and novirtual

* fix empty condition / reset

* overwrite optimizations, fix move offsets overflows

* ...erase using 0xff instead of 0

* test the theory with code, different length kv were bugged

* try to check for out-of-bounds writes / reads

* style

* trying to fix mover again

* clarify length, defend against reading len on edge

* fix uncommited rewind change

* prove space assumptions

* more concise traces, fix move condition (agrh!!!)

* slightly more internal knowledge (estimates API?)

* make sure cursor is only valid within the range

* ensure 0 does not blow things

* go back up

* cursor comments

* comments

* rewrite writes through cursor

* in del too

* estimate kv storage requirements, return available size

* move raw erase / move into a method, allow ::set to avoid scanning storage twice

* refactor naming, use in code

* amend storage slicing test

* fix crash handler offsets, cleanup configuration

* start -> begin

* eeprom readiness

* dependencies

* unused

* SPI_FLASH constants for older Core

* vtables -> templates

* less include dependencies

* gcov help, move estimate outside of the class

* writer position can never match, use begin + offset

* tweak save_crash to trigger only once in a serious crash

* doh, header function should be inline

* foreach api, tweak structs for public api

* use test helper class

* when not using foreach, move cursor reset closer to the loop using read_kv

* coverage comments, fix typo in tests decltype

* ensure set() does not break with offset

* make codacy happy again