feat(formatResult): add formatResult option

[kentcdodds]

What: Adds a formatResult option

Why: So people can format the snapshot with prettier or prettier-eslint if they want to.

How: apply formatResult function (defaults to an identity function) to the result.

[codecov-io]

Codecov Report

Merging #17 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #17   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines         103    104    +1     
  Branches       23     24    +1     
=====================================
+ Hits          103    104    +1

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

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 10d2b4f...dcf5413. Read the comment docs.