* feat: Add a new ErrorHandlerWithContext
This commit adds a new error handler, which is passed the
current context, so that you can add custom redirects or even
other kinds of responses. For example:
```go
e.Use(middleware.JWTWithConfig(middleware.JWTConfig{
SigningKey: []byte("secret"),
TokenLookup: "query:token",
ErrorHandlerWithContext: func(err error, c echo.Context) error {
// do stuff with context and err
switch err.(type) {
case jwt.ValidationError:
return c.Redirect(http.StatusSeeOther, "/login")
}
return err
},
}))
```
* chore: address golint issues