a121e19e94 hashes: Implement AsRef for fixed size arrays (Tobin C. Harding)
Pull request description:
Implement `AsRef<[u8; X]>` for hash types including wrapped hash types. Doing so means at times the compiler can no longer infer the type because we have `AsRef<[u8]` implemented also but we can use `into_inner` and `as_inner` to get the inner array if needed.
Fix: #1462
## Note
This touches code that will likely be changed by #1577 and when we do #1491 but I believe its a step forward.
ACKs for top commit:
arturomf94:
ACK [`a121e19`](a121e19e94)
apoelstra:
ACK a121e19e94
Kixunil:
ACK a121e19e94
Tree-SHA512: 257c44826c7649db25bb3a6f023f68b2f17b70c546a056afad044bc8a16bf61f654c3846222505aaf5e6f9a0ad1d2113272d61317b407d0ac83702e41060a1ee