12d615d900 Use network when calculating difficulty (Tobin C. Harding)
62af5b54f3 Improve difficulty rustdocs (Tobin C. Harding)
Pull request description:
The difficulty is a ratio of the max and current targets, since the max is network specific the difficulty calculation is also network specific.
We already have network specific maximum target constants, use them when calculating the difficulty.
Patch 1 is a trival docs improvement to `block::Header::difficulty`.
ACKs for top commit:
Kixunil:
ACK 12d615d900
apoelstra:
ACK 12d615d900
Tree-SHA512: 8b414c975306667309b0918109b3e5e8774496fc4c0f3413709e95ad7499bebf1a017def4c180a2bb5f1750c69bb505d94c738a28525b7ccc8b36e5e42514000