An ATProto PDS in Elixir

As of right now, this is not in a state where it can be used yet.

Statuses for various components:

• Identity resolution - more or less complete
• cryptographic key generation, signing, and validation - complete (secp256k1 only)
• DID PLC operation signing (CBOR) - creates complete, probably easy to add updates from here
• transforming between JSON and CBOR - complete
• Lexicon validation - not currently planned
• MST - started
• Firehose - not started
• TID generation (and decoding!!) - complete
• blobs - getBlob, listBlobs - uploadBlob held up by auth/jwt
• service proxy header - parses and finds service URL
• inter-service auth - need JWT stuff
• preferences - almost ready to start
• anything moderation-related - not started