Merging declarations and adding user-select mixing

Changes:

* merging `transition` calls
* merging `text-shadow` calls
* adding a `user-select` mixing that can handle `webkit-touch-callout` basics
* updates to docs and toc

If you want a smaller PR with just some of these changes just let's me know. Same goes for any code or style changes you would like to see - I tried to make my code/docs look like what you had in place.