Add test case link, update github template

[nhunzaker]

Adds a test reproduction link to the github issue template: https://jsfiddle.net/w2m0mang/

Also I found, when writing issues, that I spent a lot of time removing template boilerplate. I've consolidated the sections a bit. This is totally up for discussion. cc @leobauza

[codecov-io]

Codecov Report

Merging #389 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #389   +/-   ##
=======================================
  Coverage   99.77%   99.77%           
=======================================
  Files          25       25           
  Lines         881      881           
=======================================
  Hits          879      879           
  Misses          2        2

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[mackermedia]

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