implement Writer for Vec<u8>

The trait has an obvious, sensible implementation directly on vectors so
the MemWriter wrapper is unnecessary. This will halt the trend towards
providing all of the vector methods on MemWriter along with eliminating
the noise caused by conversions between the two types. It also provides
the useful default Writer methods on Vec<u8>.

After the type is removed and code has been migrated, it would make
sense to add a new implementation of MemWriter with seeking support. The
simple use cases can be covered with vectors alone, and ones with the
need for seeks can use a new MemWriter implementation.

src/libgraphviz/lib.rs

@@ -90,7 +90,7 @@ impl<'a> dot::GraphWalk<'a, Nd, Ed> for Edges {
     fn target(&self, e: &Ed) -> Nd { let &(_,t) = e; t }
 }
 
-# pub fn main() { use std::io::MemWriter; render_to(&mut MemWriter::new()) }
+# pub fn main() { render_to(&mut Vec::new()) }
 ```
 
 ```no_run
@@ -182,7 +182,7 @@ impl<'a> dot::GraphWalk<'a, Nd, Ed<'a>> for Graph {
     fn target(&self, e: &Ed) -> Nd { let & &(_,t) = e; t }
 }
 
-# pub fn main() { use std::io::MemWriter; render_to(&mut MemWriter::new()) }
+# pub fn main() { render_to(&mut Vec::new()) }
 ```
 
 ```no_run
@@ -246,7 +246,7 @@ impl<'a> dot::GraphWalk<'a, Nd<'a>, Ed<'a>> for Graph {
     fn target(&self, e: &Ed<'a>) -> Nd<'a> { let &(_,t) = e; t }
 }
 
-# pub fn main() { use std::io::MemWriter; render_to(&mut MemWriter::new()) }
+# pub fn main() { render_to(&mut Vec::new()) }
 ```
 
 ```no_run
@@ -274,7 +274,7 @@ pub fn main() {
 #![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
        html_root_url = "http://doc.rust-lang.org/nightly/")]
-#![feature(globs)]
+#![feature(globs, slicing_syntax)]
 
 pub use self::LabelText::*;
 
@@ -553,7 +553,7 @@ mod tests {
     use self::NodeLabels::*;
     use super::{Id, LabelText, LabelStr, EscStr, Labeller};
     use super::{Nodes, Edges, GraphWalk, render};
-    use std::io::{MemWriter, BufReader, IoResult};
+    use std::io::{BufReader, IoResult};
     use std::str;
 
     /// each node is an index in a vector in the graph.
@@ -702,9 +702,9 @@ mod tests {
     }
 
     fn test_input(g: LabelledGraph) -> IoResult<String> {
-        let mut writer = MemWriter::new();
+        let mut writer = Vec::new();
         render(&g, &mut writer).unwrap();
-        let mut r = BufReader::new(writer.get_ref());
+        let mut r = BufReader::new(writer[]);
         r.read_to_string()
     }
 
@@ -809,7 +809,7 @@ r#"digraph hasse_diagram {
             "branch2",
             "afterward"));
 
-        let mut writer = MemWriter::new();
+        let mut writer = Vec::new();
 
         let g = LabelledGraphWithEscStrs::new(
             "syntax_tree", labels,
@@ -817,7 +817,7 @@ r#"digraph hasse_diagram {
                  edge(1, 3, ";"),    edge(2, 3, ";"   )));
 
         render(&g, &mut writer).unwrap();
-        let mut r = BufReader::new(writer.get_ref());
+        let mut r = BufReader::new(writer[]);
         let r = r.read_to_string();
 
         assert_eq!(r.unwrap().as_slice(),