Introduce most of SDK types

[dudk]

This PR includes most of VST2 SDK types except the following categories.

Offline processing:

• VstOfflineTask
• VstOfflineTaskFlags
• VstOfflineOption
• VstVariableIo

Files handling:

• VstAudioFile
• VstAudioFileFlags
• VstAudioFileMarker
• VstFileType
• VstFileSelectCommand
• VstFileSelectType
• VstFileSelect

[codecov[bot]]

Codecov Report

Merging #33 (bb9f065) into master (a484a34) will increase coverage by 1.02%. The diff coverage is 82.35%.

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
+ Coverage   41.78%   42.80%   +1.02%     
==========================================
  Files           9        9              
  Lines         292      292              
==========================================
+ Hits          122      125       +3     
  Misses        156      156              
+ Partials       14       11       -3     

Impacted Files	Coverage Δ
opcode.go	80.76% <ø> (ø)
opcode_string.go	36.36% <ø> (ø)
sdk.go	100.00% <ø> (ø)
vst.go	51.51% <0.00%> (-3.04%)	:arrow_down:
events.go	90.32% <90.32%> (ø)
vst_darwin.go

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[dudk]

Refers #11