As implementations are refereed to GSS-API libraries as per the RFC and
GSSAPI typically refers to the SASL authentication mechanism.

...and minor rewording on the same paragraph.

... instead of duplicating info.

...and removed duplication of what protocols are supported from the
description text.

...and revised the proxy wording a little as well.

...and corrected a related typo in curl_easy_setopt.3.

As this has been present for SOCKSv5 proxy since v7.19.4 and for IMAP,
POP3 and SMTP authentication since v7.38.0.

Support for Kerberos V4 was removed in v7.33.0.

As this is covered by the PROTOCOLS section and saves having to update
two parts of the document with the same information in future.

As implementations are refereed to GSS-API libraries as per the RFC and
GSSAPI typically refers to an authentication mechanism.

Added missing IMAP to the protocol list.

...as this option affects more that just FTP.

Whilst the description included information about SMTP, the protocol
list only showed "TTP, FTP, IMAP, POP3".

Fixed the ability to use the current log-in credentials with DIGEST-MD5.
I had previously disabled this functionality in commit 607883f1 as I
couldn't get this to work under Windows 8, however, from testing HTTP
Digest authentication through Windows SSPI and then further testing of
this code I have found it works in Windows 7.

Some further investigation is required to see what the differences are
between Windows 7 and 8, but for now enable this functionality as the
code will return an error when AcquireCredentialsHandle() fails.

- Remove SSLv3 from SSL default in darwinssl, schannel, cyassl, nss,
openssl effectively making the default TLS 1.x. axTLS is not affected
since it supports only TLS, and gnutls is not affected since it already
defaults to TLS 1.x.

- Update CURLOPT_SSLVERSION doc

... and added a small example