Add 'crystal-trim-indent' command

This removes trailing whitespaces from the end of lines

rc/filetype/crystal.kak

@@ -178,6 +178,14 @@ evaluate-commands %sh[
 # Commands
 # ‾‾‾‾‾‾‾‾
 
+define-command -hidden crystal-trim-indent %{
+    evaluate-commands -no-hooks -draft -itersel %{
+        execute-keys <a-x>
+        # remove trailing white spaces
+        try %{ execute-keys -draft s \h+$ <ret> d }
+    }
+}
+
 define-command -hidden crystal-indent-on-new-line %{
     evaluate-commands -no-hooks -draft -itersel %{
         # Copy previous line indent