Using undo data for a block (rev?????.dat) we can retrieve value information about prevouts and calculate the final transaction fee (rate). This approach is about 80x faster, drops the requirement for -txindex, and works for all non-pruned blocks.
Removes medianfeerate result from getblockstats.
Adds feerate_percentiles which give the feerate of the 10th, 25th, 50th,
75th, and 90th percentile weight unit in the block.
