Added bounceout/bouncein tweens.

[Silver-Hawk]

Added standard flux style function for bounce tween.

[rxi]

Apologies for the slow response.

Although I appreciate the effort it looks like you put in -- especially with keeping with the style of the existing tween types -- I fear this addition might begin pushing the library in a direction away from "lightweight" which it maintains as one of its goals.

I'll leave the pull request open for the time being so it does not get lost. I may rework some parts of the library in the future in which case additional tween-types might find a place.

Thanks

[Jasoco]

Actually I like having the bounce option. I added the code for it from this modification to the flux.lua I have in my project and it works great. Bounce is really useful and I'd be happy if you decided to make it part of the official library. Just my two cents. I'm glad I Googled for an answer before trying to implement it myself.

[Silver-Hawk]

@Jasoco Glad you liked it :) I also use it a lot so I thought it might be useful :)
@rxi No worries, I understand why you think it's not as clean as the usual functions, but I searched the web for a cleaner version before I made it, but without luck, it can however possible be simplified :)