Splits up the `PaddingScheme` enum into four structs, named after the
previous variants of the struct (adopting capitalization from the Rust
API guidelines):
- `oaep::Oaep`
- `pkcs1v15::{Pkcs1v15Encrypt, Pkcs1v15Sign}`
- `pss::Pss`
All of these are re-exported from the toplevel.
Each of these structs impls one or more of the following traits:
- `PaddingScheme`: used for encryption
- `SignatureScheme`: used for signing
The `PaddingScheme` constructors have been remapped as follows:
- `new_oaep` => `Oaep::new`
- `new_oaep_with_label` => `Oaep::new_with_label`
- `new_oaep_with_mgf_hash` => `Oaep::new_with_mgf_hash`
- `new_oaep_with_mgf_hash_with_label` => `Oaep::new_with_mgf_hash_and_label`
- `new_pkcs1v15_encrypt` => `Pkcs1v15Encrypt`
- `new_pkcs1v15_sign` => `Pkcs1v15Sign::new`
- `new_pkcs1v15_sign_raw` => `Pkcs1v15Sign::new_raw`
- `new_pss` => `Pss::{new, new_blinded}`
- `new_pss_with_salt` => `Pss::{new_with_salt new_blinded_with_salt}`
