38005f6aa7 Use Target for pow_limit (Tobin C. Harding)
Pull request description:
The `Params::pow_limit` field is currently a `Work` type, this is incorrect. The proof of work limit is the highest _target_ not the lowest work (even though these have a relationship).
Note that we use the highest _attainable_ target, this differs from Bitcoin Core and the reasoning is already documented in the code.
Add new consts and document where they came from as well as how they differ to Core.
Use the new consts in the various network specific `Params` types.
Fix: #2106
ACKs for top commit:
junderw:
ACK 38005f6aa7
apoelstra:
ACK 38005f6aa7
Tree-SHA512: 5e71f69cdd555fd95a52fc1479e27b5e11226772f6432758c1364107a068bd1271486da6db1ece694da0287ce10cfbc18d28d6e3dbb0b9d387ff968eea43ab18
e0ddead255