Add Message.hasCaption() method

[NikMAX2077]

Is your feature request related to a problem? Please describe. I discovered that Message class has method hasText() that check message for text, but it have not similar method for media captions.

Describe the solution you'd like Method hasCaption() that return true if message has media caption and false if it's not.

Describe alternatives you've considered Of course I can check caption field for null or empty string, but it seems to me that hasCaption() method would look intuitive and checking messages for captions would not be out of general style of the library