Implement `audio` method

[fabio-ivona]

implement https://core.telegram.org/bots/api#sendaudio

to allow:

Telegraph::audio($path, $title, $performer, $duration)
    ->thumb($thumbImagePath)
    ->silent()
    ->protected()

[VividhPandey003]

Hey, I am a beginner to Open Source and really looking forward to contribute to this repo. Could you please explain this issue to me and if I'm able to, assign this issue to me

[fabio-ivona]

Hi, have you ever used our package?

[VividhPandey003]

Hii, You can just ignore my comment. I do not have knowledge to fix it right now. If someday I'm able to I'll come back to this repo to contribute. Thank You for giving me your time

[nicola-posa]

Hi, I'm implementing this one