Core functions for handling PGP objects.

This namespace provides functionality to generate PGP keypairs and keyrings
using a convenient macro syntax.

The two primary supported key types are RSA keys (via `rsa-keypair-generator`)
and Elliptic Curve keys (via `ec-keypair-generator`). A set of the supported
named curves can be found in `elliptic-curve-names`.

To generate PGP keyrings with designater master keys and subkeys with specific
roles and restrictions, use the `generate-keys` macro. This returns a map with
`:public` and `:secret` entries containing the respective keyrings.

This namespace handles interactions with PGP keyrings.

Literal keyring files are directly supported, and key servers and other
stores can extend the `KeyRing` protocol for further extension.

The functions in this namespace package raw data into PGP _messages_, which
can be compressed, encrypted, and signed.

The encryption functions use the concept of _encryptors_ and _decryptors_.
A collection of encryptors may be used to encipher a message, and any
corresponding decryptor will be able to decipher it.

For symmetric encryption, the encryptor is the passphrase string and the
corresponding decryptor is the same string.

For public-key encryption, the encryptor is the public-key object and the
decryptor is the corresponding private-key. Alternately, the decryptor can be
a function which accepts a key id and returns the corresponding private-key,
to look it up or unlock the key on demand.

The functions in this namespace generate and verify PGP signatures.

Vars which map Cloure keywords to numeric BouncyCastle tag codes.

Internal utility functions used by other namespaces.