README: rework the intro Less scary wording (similar to the wiki changes) and point to the user mailing list.

rangeobshash: minor cleanup of the obshash code We achieved minor speedup by delaying the hashing until we know it is needed.

stablerange: remove call to 'repo.revs' It turned out that the percentage of time spend parsing the revset string was two digits, so we compute de heads inline.

stablerange: reuse node calculation as much as possible We have a property cache with that value, so we just reuse it.

stablerange: adds some caching of the subranges The goal of subranges is to be as reusable as possible, so we cache the subrange relationship to take advantage of this.

stablerange: operate on an unfiltered repository We only do operation on ancestors so using unfiltered is fine.

depth: use lower lever function to compute missing The time spend parsing the revset is noticeable.

depth: update depth to code to reuse ancestors depth Computing the depth of all N revs is no longer 'O(N**2)'

obsdiscovery: extract a smarted depth in utility The function is reusing previous depth for ancestors unless this is a merge.

obsdiscovery: simply some of the missing computation