Patch by: Myk Taylor

No more use exit(3) but instead tell libcurl that no byte has been
written to let it return a `CURLE_WRITE_ERROR`. In addition, check
curl easy handle return code.

Added examples of the list command and clarified existing example URLs
following recent changes.

Updated the imap features list, corrected a typo in the smtp features
and clarified a pop3 feature.

URL examples that included the UID weren't technically correct although
would pass the curl parser.

Corrected layout issues with the POP3 and IMAP URL examples introduced
in commit cb3ae689.

Updated the POP3 sub-section to refer to message ID rather than mailbox.

Added an IMAP sub-section with example URLs depicting the specification
of mailbox, uid and section.

Fixes a typo get → git in docs/CONTRIBUTE.

* Elaborates on default values of some curl_easy_setopt() options.
* Reminds the user to cast variadic arguments to curl_easy_setopt() to
  'void *' where curl internally interprets them as such.
* Clarifies the working of the CURLOPT_SEEKFUNCTION option for
  curl_easy_setopt().
* Fixes typo 'forth' → 'fourth'.
* Elaborates on CURL_SOCKET_TIMEOUT.
* Adds some missing periods.
* Notes that the return value of curl_version() must not be passed to
  free().

* Adds several links to documentation of library functions which were
  missing.
* Marks documentation of deprecated library functions "(deprecated)".
* Removes spurious .html suffixes.

I just noticed Metalink support wasn't listed as a feature of the tool.

Schannel and darwinssl use the certificates built into the
OS to do vert verification instead of bundles. darwinssl
is thread-safe. Corrected typos in the NSS docs.

Use 'vs' directory tree given that 'vc' intended one clashes
with an already existing build target in file Makefile.dist.

This reverts commit 0e66d587.

VC6 is _very_ old and we provide working makefiles even for that
compiler. Users who build with the IDE never use that method and project
file anyway and it was just lingering in the root dir.

Added IDN and HTTP data compression as they were left out of the
document until now.

Added notes for qssl, schannel and Secure Transport supporting SSLv2,
Secure Transport supports NTLM, and axTLS does not support SSLv3.

There was also a typo; "AUTH TSL" should be "AUTH TLS".

Removed whitespace introduced in commit 5f8f20f5 that caused
formatting issues when generating the website docs.

Added SMTP, SMTPS, POP3, POP3S, IMAP and IMAPS features.

Rich Gray provided good feedback and we now clarify that you can in fact
stop a multi transfer at any point you like by removing the easy handle.

Added CURLOPT_FOLLOWLOCATION since example.com is now redirected.

Reported by: Jiri Jaburek
Bug: https://bugzilla.redhat.com/896544

Bug: https://bugzilla.redhat.com/696783

Added CURLOPT_FOLLOWLOCATION since example.com is now redirected.