add examples for empty?

Author: rwtolbert

examples/empty_63.janet

@@ -0,0 +1,11 @@
+(empty? []) # -> true
+
+(empty? [1]) # -> false
+
+(empty? @[]) # -> true
+
+(empty? @{}) # -> true
+
+(empty? "") # -> true
+
+(empty? 0) # -> error: expected iterable type, got 0