BTC Tx Fee Index

This index tracks the the median Sat/vB per block.

Derivation process:

1. Retrieve all the transaction from a block via Bitcoin Core, and derive the median Sat/vB per block.

2. The index contract stores the data cumulatively.

3. It's updated on a daily basis.

Example:

Block Number	Median Sat/vB per block	IndexBalance
0	20	20
1	13	33
2	5	38