Adding set_readahead_size setter to ReadOptions...

src/db.rs

@@ -1721,6 +1721,18 @@ impl ReadOptions {
     pub fn set_total_order_seek(&mut self, v: bool) {
         unsafe { ffi::rocksdb_readoptions_set_total_order_seek(self.inner, v as c_uchar) }
     }
+
+    /// ```
+    /// use rocksdb::{ReadOptions};
+    ///
+    /// let mut opts = ReadOptions::default();
+    /// opts.set_readahead_size(4_194_304); // 4mb
+    /// ```
+    pub fn set_readahead_size(&mut self, v: usize) {
+        unsafe {
+            ffi::rocksdb_readoptions_set_readahead_size(self.inner, v as size_t);
+        }
+    }
 }
 
 impl Default for ReadOptions {