Implemented `std::error::Error` trait for error type.

src/rocksdb.rs

@@ -14,6 +14,7 @@
 //
 
 use std::collections::BTreeMap;
+use std::error;
 use std::ffi::CString;
 use std::fmt;
 use std::fs;
@@ -117,6 +118,16 @@ impl From<Error> for String {
     }
 }
 
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        &self.message
+    }
+
+    fn cause(&self) -> Option<&error::Error> {
+        None
+    }
+}
+
 impl fmt::Display for Error {
     fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         self.message.fmt(formatter)