Add ability to pass plugins to Babel

[Comandeer]

Closes #137, closes #138.

[codecov]

Codecov Report

Merging #141 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #141   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           2      2           
  Lines          48     48           
=====================================
  Hits           48     48

Impacted Files	Coverage Δ
src/utils.js	100% <ø> (ø)	⬆️
src/index.js	100% <100%> (ø)	⬆️

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