Fix onSelect usage

[polosson]

This PR is fixing all aspects of #40:

• emit a select custom event so that we can use JSX with onSelect prop,
• keep the legacy way of passing the onSelect function prop as a callback (for retro-compatibility),
• avoid multiple executions of the onSelect callback (and "select" event) when clicking on the same tab again,
• add an example using JSX, with onSelect event handling,
• add an example of onSelect callback in existing example which use template.

I hope you'll approve this soon!

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[polosson]

Hi @egoist !
Any chance to have this little PR reviewed and merged? I really need this improvement...
Or, can you please tell us if this lib is dead?
Thanks a lot, by the way. Cheers!