Sleep command (#2381)

* Add deserialization of Primitive::Duration; Fixes #2373

* Implement Sleep command

* Add comment saying you should name your rest field "rest"

* Fix typo

* Add documentation for sleep command

docs/commands/sleep.md

@@ -0,0 +1,21 @@
+# sleep
+
+Delay for a specified amount of time
+
+Syntax: `sleep <time> [additional_time]...`
+
+## Flags
+`-h`, `--help`
+  Display help message.
+
+## Examples
+
+Sleep for 3 seconds
+```shell
+> sleep 3sec
+```
+
+Sleep for 1 minute and 2 seconds
+```shell
+> sleep 1sec 1min 1sec
+```