* Rename `sj`/`s*` and move them under `sH`. Remove `s=`
* Rename `s-*` to `sH-`
* Use `sd` for "seek delta", which moves relative to the current offset
* Enforce <cmd> <arg> syntax. So no more `s+16` but `s +16`. Command
`sHr` is for redo history, `sHu` for undo history. If one wants to move
relative to the current address, they need to do `sd +10`/`sd -10`.
* Remove `ss` commands in favour of `cmd.seek.silent`. This was anyway
used mainly for scripts, so no need to replicate all `s` commands
under `ss`.
Change a bit rz_core_seek API to avoid dupped entries in seek history.
* Remove undo write API, it was not used
* Move seek from IO to Core
* Remove IO undo files
* Fix cursor positionig in visual when doing undo/redo
* Add doxygen doc for rz_core_seek API
* Add cfg.seek.{histsize,silent} evals
* Add unit test for rz_[p]vector_foreach_prev
