Extend filter syntax with optional specification of file status: add, modified, deleted (#22)

* Add support for specification of change type (add,modified,delete)

* Use NULL as separator in git-diff command output

* Improve PR test workflow

* Fix the workflow file

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 2