Document APIs relating to configuring certificates and private keys.

The APIs that are CTRL macros will be documented (and converted to
functions) in a follow-up.

Change-Id: I7d086db1768aa3c16e8d7775b0c818b72918f4c2
Reviewed-on: https://boringssl-review.googlesource.com/5354
Reviewed-by: Adam Langley <agl@google.com>
2 files changed