Py3 bindings

Sphinx v3.3

Python3 development scripts

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.