Simplify EbmlIterator & EbmlSlice's next() methods, fix EbmlIterator generic

(they don't have dynamic buffers to worry about)

src/iterator.rs

@@ -1,7 +1,6 @@
 use std::marker::PhantomData;
 
 use ebml::FromEbml;
-use webm::WebmElement;
 
 pub struct EbmlIterator<'a, T: FromEbml<'a>>(&'a [u8], PhantomData<fn() -> T>);
 
@@ -10,17 +9,12 @@ pub fn ebml_iter<'a, T: FromEbml<'a>>(source: &'a [u8])-> EbmlIterator<'a, T> {
 }
 
 impl<'a, T: FromEbml<'a>> Iterator for EbmlIterator<'a, T> {
-    type Item = WebmElement<'a>;
+    type Item = T;
 
-    fn next(&mut self) -> Option<WebmElement<'a>> {
-        WebmElement::check_space(self.0).unwrap_or(None).and_then(|element_size| {
-            let (element_data, rest) = self.0.split_at(element_size);
-            self.0 = rest;
-            match WebmElement::decode_element(element_data) {
-                Err(_) => None,
-                Ok(None) => panic!("Buffer was supposed to have enough data to parse element, somehow did not."),
-                Ok(Some((element, _))) => Some(element)
-            }
+    fn next(&mut self) -> Option<T> {
+        T::decode_element(self.0).unwrap_or(None).and_then(|(element, element_size)| {
+            self.0 = &self.0[element_size..];
+            Some(element)
         })
     }
 }

src/slice.rs

@@ -9,19 +9,9 @@ impl<'b> EbmlEventSource for EbmlSlice<'b> {
     type Error = EbmlError;
 
     fn poll_event<'a, T: FromEbml<'a>>(&'a mut self) -> Result<Async<Option<T>>, EbmlError> {
-        T::check_space(self.0).and_then(|size_option| {
-            match size_option {
-                None => Ok(None),
-                Some(element_size) => {
-                    let (element_data, rest) = self.0.split_at(element_size);
-                    self.0 = rest;
-                    match T::decode_element(element_data) {
-                        Err(err) => Err(err),
-                        Ok(None) => panic!("Buffer was supposed to have enough data to parse element, somehow did not."),
-                        Ok(Some((element, _))) => Ok(Some(element))
-                    }
-                }
-            }
-        }).map(Async::Ready)
+        T::decode_element(self.0).map(|option| option.map(|(element, element_size)| {
+            self.0 = &self.0[element_size..];
+            element
+        })).map(Async::Ready)
     }
 }

src/webm.rs

@@ -134,7 +134,7 @@ mod tests {
 
     #[test]
     fn decode_webm_test1() {
-        let mut iter = parse_webm(TEST_FILE).into_iter();
+        let mut iter = parse_webm(TEST_FILE);
 
         // test that we match the structure of the test file
         assert_eq!(iter.next(), Some(WebmElement::EbmlHead));