Split Shamisen into smaller parts and publish NuGet packages

[MineCake147E]

Background and motivation

Currently, Shamisen is getting larger and larger, and causing code bloat because of more features and their optimization.
Some user doesn't need a fully-managed FLAC decoder while some of other doesn't need any IOs.
So I can split Shamisen into smaller parts, and bundle them in several NuGet package if needed.

Possible new library structure

• Shamisen NuGet package
  • Shamisen.Core NuGet package / library
    • Interfaces and DSP features
    • WAV decoder and encoder
  • Shamisen.IO NuGet package / library
    • IO-related interfaces
  • Shamisen.Codecs.Flac NuGet package / library
    • FLAC decoder and encoder
  • Shamisen.Pipeline NuGet package / library

Tasks

• Split library into smaller parts
• Release alpha version of each library to NuGet