Chore: Code Coverage - Githubissues

Fixes #2

Implements client-side code coverage abstraction in a "parallel test / magellan"-friendly manner.

Add coverage options for tests.
Add coverage instrumentation for library script.
Accumulate coverage data and write out to JSON objects on after
Aggregate all JSON objects to final coverage/func report for HTML / lcov / etc reports.
Send up stats to coveralls with badge.

This code could be possibly abstracted / refactored better in the future, but works pretty easily with what we've got. And it's great to see that "all the OS / browser test coverage info" all together.

/cc @geekdave @Maciek416 @exogen

... and for npm run test-func-sauce, here's our test coverage summary:

=============================== Coverage summary ===============================
Statements   : 100% ( 36/36 )
Branches     : 94.44% ( 17/18 )
Functions    : 100% ( 4/4 )
Lines        : 100% ( 36/36 )
================================================================================

walmartlabs / little-loader

Chore: Code Coverage #12