add option for color automatic selection

[conradoqg]

Hi!

I implemented a new option to make the pick-a-color automatically select the color when change it.

I also did a minor refactoring in updatePreview and created updateInput to centralize these updates.

However, I did not fix the problem caused by #47.

[conradoqg]

I forgot to copy sample.html to the build directory. Please do it for me. Thank you.

[afucher]

This is what I need!

Can accept this pull request?