Add decoding of non-compact uints

[ivan4th]

The encoder function were already there.
Also, add tests for non-compact uint encoding/decoding.

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 51.8%. Comparing base (ed76bc2) to head (b03449f).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
decoder.go	60.0%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #98     +/-   ##
========================================
+ Coverage    50.0%   51.8%   +1.8%     
========================================
  Files           6       6             
  Lines         891     906     +15     
========================================
+ Hits          446     470     +24     
+ Misses        376     363     -13     
- Partials       69      73      +4     

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[fasmat]

I'm not a big fan of how tests in encoder_test.go and decoder_test.go are structured. They are quite hard to follow because they are so indirect and generic.

I think it would be easier to maintain those tests if they would be more explicit like in my examples above and they would hardly be longer.