Upgrade to go 1.16, use go:embed for loading default rules

[caitlinelfring]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Feature / internal update

What is the current behavior? (You can also link to an open issue here)
Go 1.16 introduced the embed package to embed files directly into a go problem. I've wanted to use this since I started woke for defining and configuring the default rules. Now that go 1.16 is out, I've switched the loading of the default rules from a pre-compile go generate to the embed package. Read more here and here

What is the new behavior (if this is a feature change)?
No new behavior on the user side, but you only need to update the default.yaml file to update default rules now.

Does this PR introduce a breaking change? (What changes might users need to make due to this PR?)
No

Other information:

[codecov]

Codecov Report

Merging #60 (32c93e1) into main (67219f0) will decrease coverage by 0.39%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main      #60      +/-   ##
==========================================
- Coverage   95.87%   95.48%   -0.40%     
==========================================
  Files          19       21       +2     
  Lines         461      465       +4     
==========================================
+ Hits          442      444       +2     
- Misses         11       12       +1     
- Partials        8        9       +1     

Impacted Files	Coverage Δ
pkg/rule/default.go	33.33% <33.33%> (ø)
pkg/rule/testrule.go	100.00% <100.00%> (ø)

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