4d0d78a3af Fix typo in from_next_work_required documentation (Shing Him Ng)
5e47c4123d Update CompactTarget::from_next_work_required to take timespan as i64 (Shing Him Ng)
Pull request description:
[In Core](f7144b24be/src/pow.cpp (L56)), the timespan is defined as a signed int64. This PR will update `from_next_work_required` to take in an `i64` instead of a `u64`
Fixes#3652
ACKs for top commit:
tcharding:
ACK 4d0d78a3af
apoelstra:
ACK 4d0d78a3af2ca300c6b40348724e806bd51ef27a; successfully ran local tests
Tree-SHA512: eea33ec18b081a97ae2a22c681982ad8693200ff8de3a3fc8f46b84b5e72f41589b79140ddd79ba3fce628f1539baf8387422bcc2c6b409fcadc4c2043aa2901