added flatter, the recursive flatten script by jt

flatter.nu

@@ -0,0 +1,10 @@
+# A command to flatten many levels by using recursion
+# by @jturner 2/10/21
+# Example: sys | flatter 3
+def flatter [levels:int] {
+  if $levels > 0 {
+    flatten | flatter $(= $levels - 1)
+  } {
+    each { echo $it }
+  }
+}