* Refactored the private key protection to use standard AEAD
construction.
* Fix sanity check of decrypted block length to stay within verified
bounds
* Cleanup test harness to split into utility file (assert()); cleaned up
names of test functions.
* Fixed scrypt params to not take too long (N=2^19)
* Updated README with these changes
* added encrypt, decrypt commands (empty now)
* use command abbreviation util library
* switched to go1.13 (ed25519 now in stdlib)
* added new code to convert/manage Ed25519 keys to Curve25519
(thanks to FiloSottile/age)