I tried hard to keep the lines at 80 characters or less, but in a few
cases I had to punt and just indented the subsequent lines by 4 spaces.

A few well-placed typedefs for callback functions would really help, but
these would be part of the API, so that's probably for later.

I also took the liberty of inserting empty lines in overlong blocks to
provide some visual space.
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1956)