Updated README with error code stuff

Author: sfackler

README.md

@@ -162,7 +162,11 @@ methods, there is a second variant prefixed with `try_` which returns a
 ```rust
 match conn.try_update(query, params) {
     Ok(updates) => println!("{} rows were updated", updates),
-    Err(err) => println!("An error occurred: {}", err.to_str())
+    Err(err) => match err.code {
+        NotNullViolation => println!("Something was NULL that shouldn't be"),
+        SyntaxError => println!("Invalid query syntax"),
+        _ => println!("A bad thing happened: {}", err.message),
+    }
 }
 ```
 

src/lib.rs

@@ -19,7 +19,6 @@ use std::rt::io::net::ip::SocketAddr;
 use std::rt::io::net::tcp::TcpStream;
 
 use error::hack::PostgresSqlState;
-
 use message::{BackendMessage,
               AuthenticationOk,
               AuthenticationKerberosV5,
@@ -348,7 +347,7 @@ impl PostgresConnection {
     }
 
     pub fn try_prepare<'a>(&'a self, query: &str)
-                -> Result<NormalPostgresStatement<'a>, PostgresDbError> {
+            -> Result<NormalPostgresStatement<'a>, PostgresDbError> {
         let id = self.next_stmt_id.take();
         let stmt_name = format!("statement_{}", id);
         self.next_stmt_id.put_back(id + 1);