nghttpx: Make sure that Pool gets cleared when all buffers are returned

Added new nghttp2_ksl.c to Windows makefile

nghttpx: Choose ECDSA cert if compatible signature algorithm available

nghttpx: Add workaround to include ':' in backend pattern

Fix typo in security.rst

nghttpx: Add accesslog variables to record request path without query

This commit the following variables to construct request line without
including query component:

* $method
* $path
* $path_without_query
* $protocol_version

Copy build_config.rb to build directory because now
build_config.rb.lock is created along side it.

Define toolchain depending on CC environment variable.

This commit fixes the following warning:

RemovedInSphinx30Warning: sphinx.locale.l_() is deprecated.  Please use `_()` instead.

doc: nghttp2_session_send is also affected by max concurrent streams

Better handling of tls and early data buffer