cleanup and documentation updates

VERSION_HISTORY.md

@@ -5,6 +5,9 @@
 * **Compatibility Breaking Changes**
 	* `SigningMethodHS256` is now `*SigningMethodHMAC` instead of `type struct`
 	* `SigningMethodRS256` is now `*SigningMethodRSA` instead of `type struct`
+	* `KeyFunc` now returns `interface{}` instead of `[]byte`
+	* `SigningMethod.Sign` now takes `interface{}` instead of `[]byte` for the key
+	* `SigningMethod.Verify` now takes `interface{}` instead of `[]byte` for the key
 * Renamed type `SigningMethodHS256` to `SigningMethodHMAC`.  Specific sizes are now just instances of this type.
     * Added public package global `SigningMethodHS256`
     * Added public package global `SigningMethodHS384`

jwt.go

@@ -20,6 +20,11 @@ var TimeFunc = time.Now
 // Header of the token (such as `kid`) to identify which key to use.
 type Keyfunc func(*Token) (interface{}, error)
 
+// Error constants
+var (
+	ErrInvalidKey = errors.New("Key is invalid or of invalid type.")
+)
+
 // A JWT Token.  Different fields will be used depending on whether you're
 // creating or parsing/verifying a token.
 type Token struct {

rsa.go

@@ -18,7 +18,6 @@ var (
 	SigningMethodRS256 *SigningMethodRSA
 	SigningMethodRS384 *SigningMethodRSA
 	SigningMethodRS512 *SigningMethodRSA
-	ErrInvalidKey      = errors.New("An invalid key was passed. Expected a []byte")
 )
 
 func init() {