This adds a new plugin for HTTPS supporting HTTP version 2.0
(IETF RFC 7540), and based on the latest version of HTTP protocol
semantics (IETF RFC7230-9 series).

It provides support for seeking in a single round trip time by
reusing the same TCP connection and TLS session. It could be further
extended to reusing connections over multiple access instances,
e.g. to support segmented streaming.

It also addresses a number of protocol bugs in the existing HTTP
stack, such as handling of HTTP 100, 201 and 416 codes. It also adds
automatic safe reconnection.

Currently, the old HTTP access is favored due to a few missing
features:
- HTTP 1.1 fallback - work in progress,
- proxies (i.e. HTTP CONNECT) - work in progress,
- authentication,
- cookies.