* Allow to serialize extension values as DER bytes string.

* Prepare test for SignedCertificateTimestamps.

also document that we can return these key types in a certificate,
although they can't be self-signed of course

* Move around some code to kill the need for a backend method
* Type the backend arg to typing.Any since we just don't care now

`rfc4514_string()` and related methods now have an optional
`attr_name_overrides` parameter to supply custom OID to name mappings,
which can be used to match vendor-specific extensions.

**BACKWARDS INCOMPATIBLE:** Reverted the nonstandard formatting of email
address fields as `E` in `rfc4514_string()` methods from version 35.0.

The previous behavior can be restored with:
`name.rfc4514_string({NameOID.EMAIL_ADDRESS: "E"})`

Expanded documentation of `Name.rfc4514_string`.

* Convert CRL creation to Rust

* fixes

* small reflows

* Delete all teh code

* flake8

* Convert CSR creation to Rust

* put this back

* unused

* coverage

* Convert x.509 certificate generation to Rust

* flake8

* Coverage shenangins

* moar hashes

* moar hashes

* xxx

* The rest

* file

* first milestone!

* progress

* Good progress

* Aaaand, tests pass!

* linter fixes

* moar linting

* moar linting

* style on that coverage

* Flesh this out

* reformat

* Remove RSA+DSA support, will be added back later

* Refactor to avoid todo!() branch

* sha384 support

* Unused

* Suggesting I learn to spell? It's a bold move cotton, let's see how it pays off