Refactor API to improve functionality and usability

[maRci002]

This PR contains the following:

• Refactored API to use Future instead of promiseToFuture calls
• createFFmpeg now uses CreateFFmpegParam
• ffmpeg.run now handles List<String>
• ffmpeg.runCommand added to use one-liner command
• ffmpeg.setProgress now requires ProgressParam callback
• ffmpeg.setLogger now requires LoggerParam callback
• ffmpeg.unlink added to free up memory
• ffmpeg.readDir to read files which are handled by ffmpeg
• Updated documentation
• Updated example

I have just finished battle testing against the video_editor package

video_editor.mp4

[sarankumar-ns]

Hi @maRci002, Thank you for your contribution.