* Re-implemented `hexaryFollow()` in a more general fashion
details:
+ New name for re-implemented `hexaryFollow()` is `hexaryPath()`
+ Renamed `rTreeFollow()` as `hexaryPath()`
why:
Returning similarly organised structures, the results of the
`hexaryPath()` functions become comparable when running over
the persistent and the in-memory databases.
* Added traversal functionality for persistent ChainDB
* Using `Account` values as re-packed Blob
* Repack samples as compressed data files
* Produce test data
details:
+ Can force pivot state root switch after minimal coverage.
+ For emulating certain network behaviour, downloading accounts stops for
a particular pivot state root if 30% (some static number) coverage is
reached. Following accounts are downloaded for a later pivot state root.
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