Add write example.

examples/write.rs

@@ -0,0 +1,22 @@
+extern crate fatfs;
+
+use std::fs::OpenOptions;
+use std::io::prelude::*;
+use std::str;
+
+use fatfs::{FileSystem, FsOptions, BufStream};
+
+fn main() {
+    let img_file = match OpenOptions::new().read(true).write(true).open("fat.img") {
+        Ok(file) => file,
+        Err(err) => {
+            println!("Failed to open image: {}", err);
+            return;
+        }
+    };
+    let mut buf_stream = BufStream::new(img_file);
+    let options = FsOptions::new().update_accessed_date(true);
+    let fs = FileSystem::new(&mut buf_stream, options).unwrap();
+    let mut file = fs.root_dir().create_file("hello.txt").unwrap();
+    file.write_all(b"Hello World!").unwrap();
+}

src/dir.rs

@@ -126,7 +126,7 @@ impl <'a, 'b> Dir<'a, 'b> {
         }
     }
 
-    /// Creates new file or opens existing.
+    /// Creates new file or opens existing without truncating.
     pub fn create_file(&mut self, path: &str) -> io::Result<File<'a, 'b>> {
         let (name, rest_opt) = split_path(path);
         let r = self.find_entry(name);

src/file.rs

@@ -43,7 +43,7 @@ impl <'a, 'b> File<'a, 'b> {
         }
     }
 
-    /// Truncate file to current position.
+    /// Truncate file in current position.
     pub fn truncate(&mut self) -> io::Result<()> {
         match self.entry {
             Some(ref mut e) => {