We use `bcrypto` to compute hashes, but since this library is a bit
problematic, here we replace it with hashing algorithms from the
`ethers` library. `ethers` has no `hash160` algorithm but under the hood
`HASH160 = RIPEMD160(SHA256(X))` so it's possible to compute `hash160`
using `ethers`.

Adds basic tests to `computeHash160`, `computeHash256` and `computeScriptHash`
functions so that we are sure they are working exactly the same as when we used
`bcrypto` library inside them.