Implement Remote Control for rclone #2111

This implements a remote control protocol activated with the --rc flag
and a new command `rclone rc` to use that interface.

Still to do
  * docs - need finishing
  * tests

bin/make_manual.py

@@ -18,6 +18,7 @@ docs = [
     "docs.md",
     "remote_setup.md",
     "filtering.md",
+    "rc.md",
     "overview.md",
 
     # Keep these alphabetical by full name