Previously we wrongly handles stream per connection when h2 backend
failed or closed.  If upstream is h2 or spdy, streams which are not
associated to the failed h2 backend are also handled, which is
unnecessary.

Move DATA frame handling code to switch-case of frame type.

tls_sni returns TLS SNI value which client sent in this TLS
connection.

We added --frontend-http2-window-size,
--frontend-http2-connection-window-size, --backend-http2-window-size,
and --backend-http2-connection-window-size option to replace existing
*-bits options.  The old options are not flexible because they only
specify number of bits.  Now we can specify integer value, with
possible g, m, and k unit.  The old options are still available for
backend compatibility, but are deprecated.

This also fixes LT revision in CMakeLists.txt, which was not updated
in v1.14.0 release.

Revert part of 16c46114 to fix race
condition that incoming stream after sending GOAWAY causes connection
error.  The strict stream handling introduced in the above commit does
not handle several cases well (e.g., GOAWAY race, and refusing streams
because of concurrency limit).

std::make_shared in Xcode 7, 7.1, and 7.2 does not perform
value-initialization, and causes undefined behaviour if struct does
not have user defined default constructor.  This workaround explicitly
defines user defined default constructor, and initializes values.

As suggested in GH-674

This commit also fixes the bug that SETTINGS timer continues after
connection was closed.