WIP Progress on parsing labels

- Add parsing for motion at start of line
- Start parsing if statements
- Add first file-based parsing test
- Implement Rule for `Box<dyn Rule>`

tests/labels/find-all.txt

@@ -0,0 +1,5 @@
+'Find all the labels and their references
+:foo
+#send foo
+#if blocked n #send foo
+#if bar foo