[DOC] Reformat README.md

Remove backticks from links. Reformat and reword How to Run Unit Tests section.
cleanup
[Bugfix beta] map.has where map.length === 0 should return false not undefined.
[BUGFIX beta] Update backburner.

Compare view:
https://github.com/ebryn/backburner.js/compare/a7dcf586bc840021d7a585eabf9fd631d76c0c35...24ff580bef0f2d402474cc3d221da73ac82f09c9
Extract DAG.js
[Bugfix beta] don’t leak `-0` as a key

* some tests for NaN support
fix testing redirect to http://localhost:4200/ redirects to http://localhost:4200/tests/ for easy test access
Merge pull request #9261 from stefanpenner/more-map

More map stuff
Merge pull request #5663 from stefanpenner/fix-redirect

fix testing redirect to http://localhost:4200/ redirects to http://local...
Correct test link URL
Merge pull request #5659 from concreted/patch-2

[DOC] Reformat README.md
Add a . to increase readability 

I added a . on line 33 to separate two sentences for increase readability.
Merge pull request #9264 from johnnyliang213/patch-1

Add a . to increase readability
Merge pull request #5677 from trek/extract-dag

Extract DAG.js
[BUGFIX beta] Add cache tests and fix undefined value
Merge pull request #9266 from mmun/cache-tests

[BUGFIX beta] Add cache tests and fix undefined value