A Emacs fork implementing non-blocking and async JSONRPC support

The fork aims to fix the strugle of lsp-mode with sync Emacs core and json handling

The fork uses separate emacs threads to run the processing and then runs release_global_lock() from the C code when the processing does not involve lisp objects. There are a lot of benefits from this approach:

• UI does not block the server. Imagine that currently you have font lock running. In stock emacs that will prevent reading the process intput even if the server has alredy sent the response to the client. Note that this will improve not only emacs performance but it will improve the performance of single threaded server because the server won't be blocked to wait for IO to be read by the client.

• Server does not block the UI. Similarly, the processing of lsp-mode serialization of requests/deserialization of responses does block UI processing. Only small portion of whole JSONRPC

• Server being slow reading requests does not block the UI . In stock emacs sending requests to the server will force emacs to wait for server to read the request.

• Less garbage. Since a lot of the processing does not involve lisp objects we generate less garbage and as a result the GC runs less often.

The code runs fine with most of the servers I have tested with. Only Linux/Unix is supported for now.

Compile emacs just like normal emacs and then use the latest version of lsp-mode.

Thanks to 606u for helping me out with low level process communication code