Refactor index.js & add more tests

[mfeniseycopes]

Refactors index.js to utilize more helper methods and make code more semantic. No changes in logic or naming conventions, just shifting things around. Also, moves early returns to the top of createLogger to prevent unnecessary assignments and variable creation.

Also, adds more specs to index.spec.js (still needs more though) and moves helper tests to helpers.spec.js.

Let me know what you think!

[codecov-io]

Codecov Report

Merging #223 into master will decrease coverage by 14.21%. The diff coverage is 89.28%.

@@             Coverage Diff             @@
##           master     #223       +/-   ##
===========================================
- Coverage   83.56%   69.34%   -14.22%     
===========================================
  Files           5        5               
  Lines         146      137        -9     
===========================================
- Hits          122       95       -27     
- Misses         24       42       +18

Impacted Files	Coverage Δ
src/index.js	89.74% <89.28%> (+2.9%)	:arrow_up:
src/diff.js	8% <0%> (-92%)	:arrow_down:
src/core.js	78.68% <0%> (+2.63%)	:arrow_up:

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[imevro]

Sorry for delay, will review on this week.

[imevro]

But it looks pretty good!

[imevro]

Can you please fix merge conflicts?

[mfeniseycopes]

Renamed #noLogger to #hasLogger and rebased to resolve merge conflicts.

[mfeniseycopes]

@evgenyrodionov Have you had a chance to look this over?

[imevro]

@mfeniseycopes yes, after #234. Sorry for a delay, too busy now.