Release version `0.7.0`

[luckysori]

With this new version, we are replacing https://crates.io/crates/ark-secp256k1-zkp with a new crate ark-secp256k1 (due to #61). Alternatively, we can wait for rust-bitcoin/rust-secp256k1#794 and the subsequent release of rust-secp256k1.

[tiero]

Let's wait for full release at this point

[bonomat]

blocked by #70