Freature request: setAlpha() and getAlpha() should be chainable

[iansinnott]

It would be nice if these methods returned this. Would allow things like this:

var color = tinycolor('red').setAlpha(0.2).toString('rgb');

[mrkeyboard]

@iansinnott , I came across the same issue with setAlpha which returned undefined. In my pull request it now returns the tinyColor object. I'm not sure it makes sense to change getAlpha return value though.

[bgrins]

Yeah, getAlpha already has a return value. I think setAlpha sounds good in #48

[bgrins]

Fixed by #48

[iansinnott]

Nice job, thanks guys 👍