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>`

src/labels/snapshots/zasm__labels__labels__test__label_detection.snap

@@ -0,0 +1,9 @@
+---
+source: src/labels/labels.rs
+expression: result
+---
+'Find all the labels and their references
+:(foo)
+#send foo
+#if blocked n #send foo
+#if bar foo