README: Fix alignment.
README: Added information about project.
wrapper.sh: Added integration with dmenu and mpv.

- `add` function simply adds a channelID to the subscription list.
- `list` function gets the list, pipes it to dmenu, and then uses POSIX RegEx to
  resolve the title and video ID and pass to mpv.
- `usage` prints the commands to use the program.
wrapper.sh: Added placeholder functionality.
main.go: Ran `go fmt` for clean-up.
main.go: Removed unnecessary usage const.
main.go: Removed deprecated functions.

- Removed dmenuList, playVideo, and listVideos
  Functionality will be moved to wrapper script.
main.go: Converted to table and removed channels var.
main.go: List all videos to stdout for wrapper.
main.go: Added global CONFIG_DIR and added flags.
main.go: Implemented XDG_CONFIG_DIR.
main.go: Re-factored and added features.

- Added ability to add channel to a sub file.
- Added a constant that stores the sub filename.
- Added ability to read subs from file.
- Added a getVideos() function which retrieves videos from subs.
- Added the ability to play videos through mpv.
- Added a comparison function, so we do not have to include ID in dmenu list.
- Prettified dmenu list compared to the shell version.
- Made addSub() function check for existing files and handle accordingly.
main.go: Added initial framework.

This is just the structure for now. It has the ability of fetching the XML data
and sorting the data. Just have to add features and integrate MPV into it.