Feature: Add support for named-pipe sockets for LSPs (#3509)

* Add support for using named pipes for lsp 'socket' servers; documentation updated accordingly
* Add tests for connecting to named pipe sockets

test/dumb_named_pipe_server.py

@@ -0,0 +1,42 @@
+"""
+This Python script creates a named pipe server that does nothing but send its input
+back to the client that connects to it. Only one argument must be given, the path
+of a named pipe to bind to.
+"""
+import os
+import socket
+import sys
+
+
+def main():
+    if len(sys.argv) < 2:
+        sys.exit('You must specify a filepath')
+
+    sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    if os.path.exists(sys.argv[1]):
+        os.remove(sys.argv[1])
+    sock.bind(sys.argv[1])
+    sock.listen(0)
+
+    pid = os.fork()
+
+    if pid:
+        print(pid)
+        sys.exit()
+
+    while True:
+        connection = sock.accept()[0]
+        connection.settimeout(5)
+
+        while True:
+            try:
+                connection.send(connection.recv(1024))
+            except socket.timeout:
+                break
+
+        connection.close()
+
+
+if __name__ == "__main__":
+    main()