Mongoose 5.0

Internal core has been changed from blocking, thread-per-connection to
non-blocking, asynchronous, one thread for all.
API modification for server creation and response creation. That allowed
keep-alive support for dynamic requests, boosting the embedded performance
to 100+ thousands requests per second on a single core
(as measured on my development MacBook laptop)
Unified handling of POST requests and Websocket requests by putting a
payload into conn->content, conn->content_len attributes.
That simplified user code and eliminated the need of mg_read(),
since mongoose buffers all data prior to calling the callback
Keep-alive support is the default
Dropped SSI support and throttling support
Several configuraition parameters are gone:
- cgi_environment (replaced with MONGOOSE_CGI),
- protect_uri (not useful)
- ssi_pattern (SSI support is gone)
- throttle (throttling support is gone)
- error_log_file (not used)
- enable_keep_alive (enabled by default)
- listening_ports (renamed to listening_port)
- num_threads (core has changed to single thread)
- put_delete_auth_file (renamed to dav_auth_file)
- authentication_domain (renamed to auth_domain)
Due to the async, non-blocking nature of the core, few restrictions
are now in place:
- user callbacks must not block
- POST and Websocket data are now buffered, and cannot be huge
mongoose is now capable on listening on only one port

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