BREAKING: change methods on BufReadExt to take '&mut self'

Previously, they consumed 'self', but there is no particular reason why
they need to do that. Instead, we can borrow self mutably.

The two methods that return iterators do continue to consume 'self'
though, which matches the style used by 'std' for 'BufRead'.

bench/src/bench.rs

@@ -244,7 +244,7 @@ fn sentences(c: &mut Criterion) {
 fn byte_lines(c: &mut Criterion) {
     use bstr::io::BufReadExt;
 
-    let corpus = SUBTITLE_EN_HUGE;
+    let mut corpus = SUBTITLE_EN_HUGE;
     define(c, "bstr/for_byte_line", "ascii", corpus, move |b| {
         b.iter(|| {
             let mut count = 0;

src/io.rs

@@ -37,7 +37,7 @@ pub trait BufReadExt: io::BufRead {
     /// use bstr::io::BufReadExt;
     ///
     /// # fn example() -> Result<(), io::Error> {
-    /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
+    /// let mut cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
     ///
     /// let mut lines = vec![];
     /// for result in cursor.byte_lines() {
@@ -80,7 +80,7 @@ pub trait BufReadExt: io::BufRead {
     /// use bstr::io::BufReadExt;
     ///
     /// # fn example() -> Result<(), io::Error> {
-    /// let cursor = io::Cursor::new(b"lorem\x00ipsum\x00dolor");
+    /// let mut cursor = io::Cursor::new(b"lorem\x00ipsum\x00dolor");
     ///
     /// let mut records = vec![];
     /// for result in cursor.byte_records(b'\x00') {
@@ -123,7 +123,7 @@ pub trait BufReadExt: io::BufRead {
     /// use bstr::io::BufReadExt;
     ///
     /// # fn example() -> Result<(), io::Error> {
-    /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
+    /// let mut cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
     ///
     /// let mut lines = vec![];
     /// cursor.for_byte_line(|line| {
@@ -136,7 +136,7 @@ pub trait BufReadExt: io::BufRead {
     /// assert_eq!(lines[2], "dolor".as_bytes());
     /// # Ok(()) }; example().unwrap()
     /// ```
-    fn for_byte_line<F>(self, mut for_each_line: F) -> io::Result<()>
+    fn for_byte_line<F>(&mut self, mut for_each_line: F) -> io::Result<()>
     where
         Self: Sized,
         F: FnMut(&[u8]) -> io::Result<bool>,
@@ -170,7 +170,7 @@ pub trait BufReadExt: io::BufRead {
     /// use bstr::io::BufReadExt;
     ///
     /// # fn example() -> Result<(), io::Error> {
-    /// let cursor = io::Cursor::new(b"lorem\x00ipsum\x00dolor");
+    /// let mut cursor = io::Cursor::new(b"lorem\x00ipsum\x00dolor");
     ///
     /// let mut records = vec![];
     /// cursor.for_byte_record(b'\x00', |record| {
@@ -184,7 +184,7 @@ pub trait BufReadExt: io::BufRead {
     /// # Ok(()) }; example().unwrap()
     /// ```
     fn for_byte_record<F>(
-        self,
+        &mut self,
         terminator: u8,
         mut for_each_record: F,
     ) -> io::Result<()>
@@ -224,7 +224,7 @@ pub trait BufReadExt: io::BufRead {
     /// use bstr::io::BufReadExt;
     ///
     /// # fn example() -> Result<(), io::Error> {
-    /// let cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
+    /// let mut cursor = io::Cursor::new(b"lorem\nipsum\r\ndolor");
     ///
     /// let mut lines = vec![];
     /// cursor.for_byte_line_with_terminator(|line| {
@@ -238,7 +238,7 @@ pub trait BufReadExt: io::BufRead {
     /// # Ok(()) }; example().unwrap()
     /// ```
     fn for_byte_line_with_terminator<F>(
-        self,
+        &mut self,
         for_each_line: F,
     ) -> io::Result<()>
     where
@@ -273,7 +273,7 @@ pub trait BufReadExt: io::BufRead {
     /// use bstr::{io::BufReadExt, B};
     ///
     /// # fn example() -> Result<(), io::Error> {
-    /// let cursor = io::Cursor::new(b"lorem\x00ipsum\x00dolor");
+    /// let mut cursor = io::Cursor::new(b"lorem\x00ipsum\x00dolor");
     ///
     /// let mut records = vec![];
     /// cursor.for_byte_record_with_terminator(b'\x00', |record| {
@@ -287,7 +287,7 @@ pub trait BufReadExt: io::BufRead {
     /// # Ok(()) }; example().unwrap()
     /// ```
     fn for_byte_record_with_terminator<F>(
-        mut self,
+        &mut self,
         terminator: u8,
         mut for_each_record: F,
     ) -> io::Result<()>