Fix coping and moving files around using the file tree (#568)

* Implement write/read buffers in electron fill

This makes cutting and copy files from the file tree work.

* Implement fs.createReadStream

This is used by the file tree to copy files.

* Allow passing proxies back from client to server

This makes things like piping streams possible.

* Synchronously bind to proxy events

This eliminates any chance whatsoever of missing events due to binding
too late.

* Make it possible to bind some events on demand

* Add some protocol documentation

packages/protocol/test/child_process.test.ts

@@ -10,7 +10,7 @@ describe("child_process", () => {
 	const cp = client.modules[Module.ChildProcess];
 
 	const getStdout = async (proc: ChildProcess): Promise<string> => {
-		return new Promise((r): Readable => proc.stdout!.on("data", r))
+		return new Promise((r): Readable => proc.stdout!.once("data", r))
 		.then((s) => s.toString());
 	};