implement a new sprout command line options mechanism

hack/dev/configs/shell.sprout.toml

@@ -0,0 +1,11 @@
+version = 1
+
+[extractors.boot.filesystem-device-match]
+has-item = "\\EFI\\BOOT\\shell.efi"
+
+[actions.chainload-shell]
+chainload.path = "$boot\\EFI\\BOOT\\shell.efi"
+
+[entries.xen]
+title = "Boot Shell"
+actions = ["chainload-shell"]