New version after fork

Major changes to original fork (May 2021):

• Renamed to 'BetterAudio.js'
• Refactured code to enable multiple player instances on same HTML page
• Scoped CSS within .better-audio class
• Added resize observer to player element to set CSS classes 'ba-large', 'ba-medium', 'ba-small', 'ba-tiny'
• Style optimizations