Bundle minified Tippy code with distribution

[BrianSipple]

After merging #261, we should be able to update the build configuration and just bundle the minified tippy script with our own distributed file.

A few benefits:

• Simplifying usage for users
• Closing Add minified js + css to release package #258
• Allowing us to know which versions of shepherd support which versions of Tippy

[RobbieTheWagner]

@BrianSipple that would not close #258. That person wanted shepherd.js etc listed as files on the releases in GitHub, so they could just quickly download them. We should decide on that separately.