b3f122b399 Add Timestamp newtype (Tobin C. Harding)
Pull request description:
Bitcoin block headers have a timestamp. Currently we are using a `u32`. While this functions correctly it gives the compiler no chance to enforce type safety.
Add a `Timestamp` newtype that is a thin wrapper around a `u32`. Document it and test the API surface in `api.rs`.
ACKs for top commit:
apoelstra:
ACK b3f122b3996c1a73479be2f95b7f2ae642c9c56f; successfully ran local tests
Kixunil:
ACK b3f122b399
Tree-SHA512: 6f4a4a588bc836243ae28f3d36be6c0ae264cb2b7a0061277910b107d05e5ca0e679497d2890208f5d8ec148f37bf263bcd0b0410f9e5e6370d8e763ff30b78a