Merge #10199: Better fee estimates

Merge #10199: Better fee estimates

38bc1ec Make more json-like output from estimaterawfee (Alex Morcos)
2d2e170 Comments and improved documentation (Alex Morcos)
ef589f8 minor cleanup: remove unnecessary variable (Alex Morcos)
3ee76d6 Introduce a scale factor (Alex Morcos)
5f1f0c6 Historical block span (Alex Morcos)
aa19b8e Clean up fee estimate debug printing (Alex Morcos)
10f7cbd Track first recorded height (Alex Morcos)
3810e97 Rewrite estimateSmartFee (Alex Morcos)
c7447ec Track failures in fee estimation. (Alex Morcos)
4186d3f Expose estimaterawfee (Alex Morcos)
2681153 minor refactor: explicitly track start of new bucket range and don't update curNearBucket on final loop. (Alex Morcos)
1ba43cc Make EstimateMedianVal smarter about small failures. (Alex Morcos)
d3e30bc Refactor to update moving average on fly (Alex Morcos)
e5007ba Change parameters for fee estimation and estimates on all 3 time horizons. (Alex Morcos)
c0a273f Change file format for fee estimates. (Alex Morcos)

Tree-SHA512: 186e7508d86a1f351bb656edcd84ee9091f5f2706331eda9ee29da9c8eb5bf67b8c1f2abf6662835560e7f613b1377099054f20767f41ddcdbc89c4f9e78946d