Added % switch and %-based translate

Allow flipsnap to get real-time measurements of elements before applying transform, and use %-based calculations based on ratio of how many items are in each 'flip' vs. how many items there are total. See comments for example.
Update flipsnap.js
Create resize-update.js

Force Flipsnap value updates whenever the page is resized to avoid having the flipsnap shifting out of place or using old measurements.
Update README.md
Update resize-update.js
Merge pull request #40 from atwixtor/master

Add a bit of responsiveness by recalculating values on resize