Add support for TLSv1.1 and TLSv1.2 options and methods

Add support for TLSv1.1 and TLSv1.2 options and methods

When OpenSSL v1.0.1+ is being built against.

Also update the documentation for sslproxy_version which was not
mentioning what the supported version codes were.

Future work:
* make version config option(s) accept a set of named versions and
  convert to codes internally.
* redesign how version and options are handled. Admin should be able to
  just list the TLSv* wanted and Squid figure out the appropriate options
  from there.