This commit drops the 'ua_' prefix and changes the public includes
to the form `#include <open62541/server.h>` instead of the old
`#include <ua_server.h>`
Make use of EXIT_SUCCESS and EXIT_FAILURE from stdlib.h.
The previous approach of returning a value from UA_StatusCode
was often broken as an exit code can (portably) only be between 0 and 125.
This commit adds asynchronous services to open62541 on client side
* Asynchronous service (highlevel read/write) are available through the API that is defined in
ua_client_highlevel_async.h
* Besides the services, the connection procedure is asynchronous as well.
* A client Application that uses the asynchronous API
adds requests by calling an asynchronous service (e.g., UA_Client_sendAsyncReadRequest(), UA_Client_sendAsyncBrowseRequest() )
checks for response with UA_Client_run_iterate() repeatedly
and processes the responses with user-defined callbacks
