Add support for web workers

[kitsonk]

Type: feature

The following has been addressed in the PR:

• There is a related issue
• All code matches the style guide
• Unit or Functional tests are included in the PR

Description:

This allows the loader to load modules when running in a web worker environment.

Resolves #115

[codecov-io]

Codecov Report

Merging #117 into master will decrease coverage by -1.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #117      +/-   ##
==========================================
- Coverage   84.97%   83.91%   -1.06%     
==========================================
  Files           1        1              
  Lines         539      547       +8     
  Branches      134      136       +2     
==========================================
+ Hits          458      459       +1     
- Misses         34       41       +7     
  Partials       47       47

Impacted Files	Coverage Δ
_build/src/loader.ts	83.91% <0%> (-1.06%)	❌

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[kitsonk]

There is an issue in that when the loader is run in a web worker, its coverage information isn't exposed. So while there is a functional test as part of this PR, it is showing that code is not covered. I suspect it would be a change to intern to post out coverage information from a web worker -> runner -> intern server.

[kitsonk]

Opened theintern/intern#721

[dylans]

Looks reasonable to me, but you may want someone else to review.