Start working on a better shell mechanism for Windows

It uses a Perl script to keep a bash session open, which attaches to a
port the game keeps open. This avoids having to start a new Git bash for
each command, improving the execution speed by a factor of 3-4.

scenes/tcp_server_shell.gd

@@ -0,0 +1,50 @@
+extends Node
+
+signal data_received(string)
+signal new_connection
+
+export var port: int
+
+var _s = TCP_Server.new()
+var _c
+var _connected = false
+
+func _ready():
+	start()
+
+func start():
+	_s.listen(port)
+		
+func _process(_delta):
+	if _s.is_connection_available():
+		if _connected:
+			_c.disconnect_from_host()
+			helpers.crash("Dropping active connection")
+		_c = _s.take_connection()
+		_connected = true
+		emit_signal("new_connection")
+		print("connected!")
+	
+	if _connected:
+		if _c.get_status() != StreamPeerTCP.STATUS_CONNECTED:
+			_connected = false
+			print("disconnected")
+#		var available = _c.get_available_bytes()
+#		while available > 0:
+#			var data = _c.get_utf8_string(available)
+#			emit_signal("data_received", data)
+#			available = _c.get_available_bytes()
+
+func send(text):
+	if _connected:
+		_c.put_utf8_string(text)
+		var response = _c.get_utf8_string()
+		var exit_code = _c.get_u32()
+		
+		var shell_command = ShellCommand.new()
+		shell_command.command = text
+		shell_command.output = response
+		shell_command.exit_code = exit_code
+		return shell_command
+	else:
+		helpers.crash("Trying to send data on closed connection")