v2.2.2

Major refactoring, thanks to the fantastic work made by Yvain Liechti).

• This is now a real jQuery plugin.
• Added RTL support for keyboard.
• Updated base structure (Hx with js-accordion__header must be now in div with js-accordion__panel).
• Added support for UMD.
• fixed an issue on multi-selectable option.
• fixed an issue in case of nested accordion.
• Added linters support, etc.