Make Tag Small

**Status**: *Review*
**Reviewers**: @jansepar 
**JIRA**: [PROD-1266](https://mobify.atlassian.net/browse/PROD-1266)
  
## Changes
- Adds JSDoc comments to aid in minification
- Rewritten to be slightly more amendable to minification
- Renamed some variables to `pre`, `post`, and `mode` to save a little bit of space.
- Split up tests to run on the full minified, and the mostly-minified (exposed) forms.
  
## How to test-drive this PR
- Runs tests (locally, and on saucelabs)
- Create tag and test it
  
## Research resources
- https://developers.google.com/closure/compiler/docs/js-for-compiler