Feature Request: Hide Cursor

[RubenSandwich]

According to the Java lanterna if you set the cursor to null it will hide the cursor: https://github.com/mabe02/lanterna/blob/release/2.1/src/main/java/com/googlecode/lanterna/screen/Screen.java#L121.

However, This doesn't work Clojure lanterna because you hit a null pointer exception because x and y are undefined: https://github.com/MultiMUD/clojure-lanterna/blob/master/src/lanterna/screen.clj#L132.

Do you have any plans on adding this feature to clojure-lanterna? I'd love to add it through a pull request but I'm pretty new to Clojure and I'm pretty sure my code would be ugly and nonidiomatic.