Updates to latest librespot, bringing along some larger changes under the hood.

Maintenance

• Display error when command can not be parsed (#161)
• Add rounding to volume percentage display (#493)
• Log warning instead of panicking on invalid color (#498)
• Update to librespot 0.2.0
  • As part of this, a lot of the Future implementations were migrated to async/.await and cleaned up
• Flip play/pause indicators (#511)

Features

• Add audio_cache_size to set maximum cache size (#429)