reexport crypto/phc_encoding

[x13a]

Make phc_encoding public available in crypto.pwhash.phc_format. It is useful for serialization password hash functions that not available in std.

/cc @jedisct1

[jedisct1]

Other serialization formats required for cryptographic operations may be good to have (S2V, constant-time hex/b64, PEM, etc).

So, instead of having all these in the top-level crypto namespace, how about a crypto.codecs or crypto.serialization namespace?

[jedisct1]

Well... phc_format is really only useful in the context of password hashing functions, so having the relevant codecs exported here is intuitive.

So let's merge this :) And maybe reexport it in a codecs namespace once there is a justification for it.

Thanks!

[jedisct1]

(looking at the diff, I originally thought it was in the top-level namespace, but it is actually in crypto.pwhash, so... this is fine 😄)