The module allows to use HTTP/2 protocol for proxying.
HTTP/2 proxying is enabled by specifying "proxy_http_version 2".

Example:

    server {
        listen 8000;

        location / {
            proxy_http_version 2;
            proxy_pass https://127.0.0.1:8443;
        }
    }

    server {
        listen 8443 ssl;
        http2 on;

        ssl_certificate certs/example.com.crt;
        ssl_certificate_key certs/example.com.key;

        location / {
            return 200 foo;
        }
    }

Chunked transfer encoding, since originally introduced in HTTP/1.1
in RFC 2068, is specified to use CRLF as the only line terminator.

Although tolerant applications may recognize a single LF, formally
this covers the start line and fields, and doesn't apply to chunks.
Strict chunked parsing is reaffirmed as intentional in RFC errata
ID 7633, notably "because it does not have to retain backwards
compatibility with 1.0 parsers".

A general RFC 2616 recommendation to tolerate deviations whenever
interpreted unambiguously doesn't apply here, because chunked body
is used to determine HTTP message framing; a relaxed parsing may
cause various security problems due to a broken delimitation.
For instance, this is possible when receiving chunked body from
intermediates that blindly parse chunk-ext or a trailer section
until CRLF, and pass it further without re-coding.

If request URI was shorter than location prefix, as after replacement
with try_files, location length was used to copy the remaining URI part
leading to buffer overread.

The fix is to replace full request URI in this case.  In the following
configuration, request "/123" is changed to "/" when sent to backend.

    location /1234 {
        try_files /123 =404;
        proxy_pass http://127.0.0.1:8080/;
    }

Closes #983 on GitHub.

The function interface is changed to follow a common approach
to other functions used to setup SSL_CTX, with an exception of
"ngx_conf_t *cf" since it is not bound to nginx configuration.

This is required to report and propagate SSL_CTX_set_ex_data()
errors, as reminded by Coverity (CID 1668589).