This PR introduces per channel context so that we can speed up operations like
retrieving the channel name from its id, or knowing what shall be done for a
packet (no config ACL recomputation at each packet).
The proxy server component might receive input related events
before the proxy client has established the connection to the
target machine.
With this change, the current keyboard state is cached and sent
to the target when it is ready. All input events received before
the target is ready are discarded.
* Split out proxy headers and moved to public API to allow external
modules to be built.
* Split proxy into proxy library and proxy binary. The library
can be used by other applications and provides a simple API
* Improved channel passthrough, now all channels including dynamic
channels work.
* Extended module API to hook more events, improved module samples
* Cleaned up proxy code, removed global static variables used,
added WINPR_ASSERT
