Fix formatting and minor restructuring

Fixed formatting using cargo fmt.
Change some parser structure to reduce code deduplication

examples/ancient-entity.rs

@@ -3,7 +3,11 @@ const DATA: &[u8] = include_bytes!("../testfiles/de_ancient.dem");
 fn main() {
     let container = csdemo::Container::parse(DATA).unwrap();
 
-    let output = csdemo::parser::parse(csdemo::FrameIterator::parse(container.inner), csdemo::parser::EntityFilter::all()).unwrap();
+    let output = csdemo::parser::parse(
+        csdemo::FrameIterator::parse(container.inner),
+        csdemo::parser::EntityFilter::all(),
+    )
+    .unwrap();
 
     println!("Header: {:?}", output.header);
     println!("Players: {:?}", output.player_info);