Bug fix for connection manager refcount issue

• Bugfix: the refcount for connection manager will pop up from zero in some situation from the culling task, which will cause destroy to happen twice and crash.

HTTP/2 Stream Manager

• Introduce HTTP/2 stream manager

HTTP/2 Message support

• Support HTTP/2 message type, instead of translating all the request to HTTP/2 format
• BUGFIX: raise proper error when reaching max concurrent stream.

Const added to members, chunked trailer support to HTTP/1, HTTP2 headers

HTTP2 headers

• pseudo headers are pushed into the front of the array list, and other than that, it will be treated the same as normal headers
• Trade off:
  • We know that push front to the array list is expensive. But, it should be used only few times, as you don't want to change pseudo headers a lot and there are at most 4 of them. More than that, we don't need to do the push front later when we need to send the headers into the wire.
  • The advantage of it is that we will have the mostly the same behavior as netty, which is used by Java SDK team already.
• add will push the pseudo header to the front of the list when needed (the last header is NOT pseudo header)

Chunked trailer

• Add chunked trailer support to HTTP/1

Const changes

• const added to aws_socket_options
• const added to aws_http_proxy_options
• const added to aws_tls_connection_options

Removed OOM conditions/tests

removed OOM test, since that's no longer allowed, (#343)

* removed OOM test, since that's no longer allowed,

BYO_CRYPTO fix and proxy environment variable fix

v0.6.7

BYO_CRYPTO test and fix (#337)

Proxy environment variable support

• Proxy environment variable support HTTP_PROXY and HTTPS_PROXY
• When enabled:
  • env HTTPS_PROXY/https_proxy will be checked when the main connection use tls.
  • env HTTP_PROXY/http_proxy will be checked when the main connection NOT use tls.
  • The lower case version has precedence.
• Metrics exposure
• Http2 on going supports

Address GCC11 warnings

v0.6.5

Fix GCC11 warnings (#326)

More validation of HTTP/1.1 messages

More validation of HTTP/1.1 messages. (#321)

Add validation for the following, according to the ABNF defined in RFC-7230.
- header field-names
- header field-values
- request method
- request-path aka URI
- response reason-phrase

Previously, we did an OK job validating incoming messages, but did no validation whatsoever of outgoing messages.

Caveats:
- URI validation is extremely basic for now.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Http proxy socket channel support

• Adds a new API for creating a socket channel through an http proxy, allowing for arbitrary protocols to establish a connection through such a proxy