Various doc fixes from GH pull requests

Thanks, folks!
        348 Benjamin Kaduk
        317 Christian Brueffer
        254 Erik Tews
        253 Erik Tews
        219 Carl Mehner
        155 (ghost)
        95 mancha
        51 DominikNeubauer

(Manually picked from 59c554b36e39256ac2cfc34dca052453e10c6d9c)
Reviewed-by: Dr. Stephen Henson <steve@openssl.org>