Use simple Promise-based API.

Split utility functions to separate file. Group all the utilities being
used by video type.

Normalize file extension when getting download.

Refactor code for cleaner codebase.

Use appropriate names for some things.

Use --force-keyframes-at-cuts to have a smooth cut.

Use cache for sending previously downloaded videos

Use postprocessor to download video to conserve data.

Remove ffmpeg hard dependency.

Add files from pridepack.