Add dotnet5.4 framework

[304NotModified]

Add dotnet5.4, update to NLog 4.4 beta1 (minimal)

fixes #49

[codecov-io]

Current coverage is 49.69%

Merging #50 into master will not affect coverage as of 084d763

@@            master     #50   diff @@
======================================
  Files           14      14       
  Stmts          163     163       
  Branches        28      28       
  Methods          0       0       
======================================
  Hit             81      81       
  Partial          8       8       
  Missed          74      74       

Review entire Coverage Diff as of 084d763

---

Uncovered Suggestions

1. +3.68% via ...ringTargetWrapper.cs#195...200
2. +3.68% via ...ringTargetWrapper.cs#167...172
3. +3.07% via ...ringTargetWrapper.cs#89...93
4. See 7 more...

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