0.8.1 restore errors not to break compatibility

Author: maciejhirsz

src/error.rs

@@ -11,7 +11,9 @@ pub enum JsonError {
     },
     UnexpectedEndOfJson,
     FailedUtf8Parsing,
+    ArrayIndexOutOfBounds,
     WrongType(String),
+    UndefinedField(String),
 }
 
 impl JsonError {
@@ -33,7 +35,9 @@ impl fmt::Display for JsonError {
 
             UnexpectedEndOfJson   => write!(f, "Unexpected end of JSON"),
             FailedUtf8Parsing     => write!(f, "Failed to parse UTF-8 bytes"),
+            ArrayIndexOutOfBounds => write!(f, "Array index out of bounds!"),
             WrongType(ref s)      => write!(f, "Wrong type, expected: {}", s),
+            UndefinedField(ref s) => write!(f, "Undefined field: {}", s)
         }
     }
 }
@@ -45,7 +49,9 @@ impl Error for JsonError {
             UnexpectedCharacter { .. } => "Unexpected character",
             UnexpectedEndOfJson        => "Unexpected end of JSON",
             FailedUtf8Parsing          => "Failed to read bytes as UTF-8 from JSON",
+            ArrayIndexOutOfBounds      => "Array index out of bounds!",
             WrongType(_)               => "Wrong type",
+            UndefinedField(_)          => "Undefined field",
         }
     }
 }