stablerange: support loading the cache iteratively We record how far we loaded so that we can resume from this point.

stablerange: add some basic documentation about the cache

stablerange: warmup all upto a revision Let us start doing more systemic warming of the cache before we start writing things out. This prepare on disk caching.

debugstablerange: add a --verify flag to the command This should help us finding bugs.

stablerange: add a proper debugstablerange commands This commands allows to inspect the standard stable range of a range. That should come handy.

debugobshashrange: add a --subranges option We stop displaying -everything- by default, since is is usually very large. This will help getting better timing when measuring cache effect too, since we won't need to dig out deep cache value that real life usage would not touch.