Add a property interface to ZstdCompressor, add ZstdError type

[mkitti]

Allow compression parameters to be set as properties

Redo of #48 from the correct branch

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 39.46%. Comparing base (89cd7ed) to head (34977a7).

Files	Patch %	Lines
src/compression.jl	47.82%	12 Missing ⚠️
src/libzstd.jl	93.75%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
+ Coverage   36.96%   39.46%   +2.50%     
==========================================
  Files           5        5              
  Lines         560      598      +38     
==========================================
+ Hits          207      236      +29     
- Misses        353      362       +9     

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