x/crypto: Add pkcs12 package for reading pkcs12 data

Package pkcs12 provides some Go implementations of PKCS#12.
This implementation is distilled from https://tools.ietf.org/html/rfc7292 and
referenced documents. It is intented for decoding P12/PFX-stored certificate+key
for use with the crypto/tls package.

Package includes @dgryski's RC2 implementation as a sub package as requested in
https://github.com/golang/go/issues/10621.

Change-Id: I78401241e39cd0099e9082a3a227cf0a3a36e6d1
Reviewed-on: https://go-review.googlesource.com/11986
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
15 files changed