Code tag patched, youtube tag replaced with video tag

- No more parsed BBCode within code tag #1 
- Removed `[youtube]` and `[yt]` deprecated tags #6 
- Syntax page updated
- `[twitter]` tag support added #6 
- `[music]` tag support added: `soundcloud`, `spotify`, `deezer` #6 
- `[video]` tag full support: `youtube.com`, `youtu.be`, `facebook.com`, `vimeo.com`, `dailymotion.com`, `dai.ly` #6