add progress bar for transcribe loop

[fcakyon]

edit: you no longer have to accept this PR, just created a new package including this feature: https://github.com/fcakyon/pywhisper

This PR adds a simple tqdm progress bar to the while loop in transcribe function.

It shows the estimated time and current progress.

[jongwook]

Good idea! It also provides means to show the transcription speed / ETA. To avoid mixing up the transcription output, I made an edit to enable the progress bar only when the verbose option is False. It's technically a breaking change but hopefully nobody minds.