Closes #1125

Now all options are in the new system.

Moved over to the new format

There's mostly likely no need to allow setting SSLv2/3 version for HTTPS
proxy. Those protocols are insecure by design and deprecated.

Also define it in ILE/RPG binding.

Closes #1142

Add missing tests for CURLINFO_SCHEME, CURLINFO_PROTOCOL, %{scheme},
and %{http_version}

closes #1143

Follow-up to 4f8b1774

Sorted the lists too.

... and include the new ones in the PDF and HTML generation targets

Closes #1141

Prior to this change we depended on errno if strtol could not perform a
conversion. POSIX says EINVAL *may* be set. Some implementations like
Microsoft's will not set it if there's no conversion.

Ref: https://github.com/curl/curl/commit/ee4f7660#commitcomment-19658189

Ref: https://github.com/curl/curl/pull/1064#issuecomment-260052409

Follow-up to dbadaebf which changed the style.

- Restore the removed parts of the parameter check.

Follow-up to 945f60e8 which altered the parameter check.

Adds access to the effectively used protocol/scheme to both libcurl and
curl, both in string and numeric (CURLPROTO_*) form.

Note that the string form will be uppercase, as it is just the internal
string.

As these strings are declared internally as const, and all other strings
returned by curl_easy_getinfo() are de-facto const as well, string
handling in getinfo.c got const-ified.

Closes #1137

Detects (char*) and 'char*foo' uses.

Verifies a 'char *name' style, with no space after the asterisk.

Coverity CID 1394666

It builds and runs all test cases. No adaptations for actual HTTPS proxy
support has been made.

vtls/gtls.c: In function ‘Curl_gtls_data_pending’:
vtls/gtls.c:1429:3: error: this ‘if’ clause does not guard... [-Werror=misleading-indentation]
   if(conn->proxy_ssl[connindex].session &&
      ^~
      vtls/gtls.c:1433:5: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the ‘if’
           return res;

* HTTPS proxies:

An HTTPS proxy receives all transactions over an SSL/TLS connection.
Once a secure connection with the proxy is established, the user agent
uses the proxy as usual, including sending CONNECT requests to instruct
the proxy to establish a [usually secure] TCP tunnel with an origin
server. HTTPS proxies protect nearly all aspects of user-proxy
communications as opposed to HTTP proxies that receive all requests
(including CONNECT requests) in vulnerable clear text.

With HTTPS proxies, it is possible to have two concurrent _nested_
SSL/TLS sessions: the "outer" one between the user agent and the proxy
and the "inner" one between the user agent and the origin server
(through the proxy). This change adds supports for such nested sessions
as well.

A secure connection with a proxy requires its own set of the usual SSL
options (their actual descriptions differ and need polishing, see TODO):

  --proxy-cacert FILE        CA certificate to verify peer against
  --proxy-capath DIR         CA directory to verify peer against
  --proxy-cert CERT[:PASSWD] Client certificate file and password
  --proxy-cert-type TYPE     Certificate file type (DER/PEM/ENG)
  --proxy-ciphers LIST       SSL ciphers to use
  --proxy-crlfile FILE       Get a CRL list in PEM format from the file
  --proxy-insecure           Allow connections to proxies with bad certs
  --proxy-key KEY            Private key file name
  --proxy-key-type TYPE      Private key file type (DER/PEM/ENG)
  --proxy-pass PASS          Pass phrase for the private key
  --proxy-ssl-allow-beast    Allow security flaw to improve interop
  --proxy-sslv2              Use SSLv2
  --proxy-sslv3              Use SSLv3
  --proxy-tlsv1              Use TLSv1
  --proxy-tlsuser USER       TLS username
  --proxy-tlspassword STRING TLS password
  --proxy-tlsauthtype STRING TLS authentication type (default SRP)

All --proxy-foo options are independent from their --foo counterparts,
except --proxy-crlfile which defaults to --crlfile and --proxy-capath
which defaults to --capath.

Curl now also supports %{proxy_ssl_verify_result} --write-out variable,
similar to the existing %{ssl_verify_result} variable.

Supported backends: OpenSSL, GnuTLS, and NSS.

* A SOCKS proxy + HTTP/HTTPS proxy combination:

If both --socks* and --proxy options are given, Curl first connects to
the SOCKS proxy and then connects (through SOCKS) to the HTTP or HTTPS
proxy.

TODO: Update documentation for the new APIs and --proxy-* options.
Look for "Added in 7.XXX" marks.