Fix receiving stream data stall

Enable session_create_idle_stream test, fix errors

Previously, if automatic window update is enabled (which is default),
after window size is set to 0 by
nghttp2_session_set_local_window_size, once the receiving window is
exhausted, even after window size is increased by
nghttp2_session_set_local_window_size, no more data cannot be
received.  This is because nghttp2_session_set_local_window_size does
not submit WINDOW_UPDATE.  It is only triggered when new data arrives
but since window is filled up, no more data cannot be received, thus
dead lock happens.

This commit fixes this issue.  nghttp2_session_set_local_window_size
submits WINDOW_UPDATE if necessary.

https://github.com/curl/curl/issues/4939

Bump llhttp to 2.0.4

Add the currently-unused `test_nghttp2_session_create_idle_stream()`
function to the test suite definition.

Modify the test in two places to make it pass:

  * Use stream ID=10 as the priority stream ID to test automatic creation
    of streams for priority specs. The code below checks against stream
    ID=10 so I assume this was a typo in the test.

  * Set the `last_sent_stream_id` instead of the `next_stream_id` to test
    that idle streams cannot be created with smaller numbers than the
    most-recently-seen stream ID. Looking at the validation path in
    `session_detect_idle_stream()`, I think this was another test typo.

lib/CMakeLists.txt: Make hard-coded static lib suffix optional

It can be set via the `STATIC_LIB_SUFFIX` variable.

This fixes every existing dependent project that relied on the name
having no suffix and thus capable of using either a static or shared
flavour depending on which one is present on this or how the linker
is configured.

Ref: https://github.com/nghttp2/nghttp2/pull/1394

Add nghttp2_check_authority as public API

Fix the bug that stream is closed with wrong error code

priority_spec::valid(): remove const qualifier from return value

This commit fixes the bug that stream is closed with wrong error code
(0).  This happens when STREAM or DATA frame with END_STREAM flag set
is received and it violates HTTP messaging rule (i.e., content-length
does not match) and the other side of stream has been closed.  In this
case, nghttp2_on_stream_close_callback should be called with nonzero
error code, but previously it is called with 0 (NO_ERROR).

gcc generates warning:
* type qualifiers ignored on function return type [-Wignored-qualifiers]

Faster Huffman encoding/decoding

Avoid filename collision of static and dynamic lib

Add new flag ENABLE_STATIC_CRT for Windows

Renames the output of the ENABLE_STATIC_LIB library/archive output
to nghttp2_static.lib/.a to avoid filenames colliding with the output
name for ENABLE_SHARED_LIB library/archive, when both are enabled.
Signed-off-by: William A Rowe Jr <wrowe@pivotal.io>
Signed-off-by: Yechiel Kalmenson <ykalmenson@pivotal.io>

Previously, mruby context is wrongly shared by multiple patterns if
the underlying SharedDownstreamAddr is shared by multiple
DownstreamAddrGroups.  This commit fixes it.

This change adds the CMake option;

  ENABLE_STATIC_CRT  Build libnghttp2 against the MS LIBCMT[d]

This avoids linking to msvcrt.lib for binaries to compile (/MT[d])
and link against the static C Runtime libcrt.lib, and
avoiding the msvcrt[d].dll dependency.
Signed-off-by: William A Rowe Jr <wrowe@pivotal.io>
Signed-off-by: Yechiel Kalmenson <ykalmenson@pivotal.io>

This is the second attempt.  The first attempt was
8a59ce6d and it failed.

This reverts commit 8a59ce6d.