Keep dependency versions compatible with the dependencies used by rust-bitcoin

[benma]

If my project uses the latest rust-bitcoin version (currently 0.31.2) and this crate, I expect to not compile the same dep twice for different versions.

Currently this is the case for bech32 - rust-bitcoin v0.31.2 uses bech32 0.10.0-beta, while this crate uses bech32 0.9.

This could be solved by using the bitcoin dep directly too, see #53