Added str::char_offset_iter() and str::rev_char_offset_iter()

Renamed bytes_iter to byte_iter to match other iterators
Refactored str Iterators to use DoubleEnded Iterators and typedefs instead of wrapper structs
Reordered the Iterator section
Whitespace fixup
Moved clunky `each_split_within` function to the one place in the tree where it's actually needed
Replaced all block doccomments in str with line doccomments

src/test/run-pass/linear-for-loop.rs

@@ -16,7 +16,7 @@ pub fn main() {
     assert_eq!(y, 6);
     let s = ~"hello there";
     let mut i: int = 0;
-    for s.bytes_iter().advance |c| {
+    for s.byte_iter().advance |c| {
         if i == 0 { assert!((c == 'h' as u8)); }
         if i == 1 { assert!((c == 'e' as u8)); }
         if i == 2 { assert!((c == 'l' as u8)); }

src/test/run-pass/utf8.rs

@@ -41,7 +41,7 @@ pub fn main() {
 
     fn check_str_eq(a: ~str, b: ~str) {
         let mut i: int = 0;
-        for a.bytes_iter().advance |ab| {
+        for a.byte_iter().advance |ab| {
             info!(i);
             info!(ab);
             let bb: u8 = b[i];