v2.0.0

• PureScript v0.15.4
• Header optics have been added; profunctor-lenses is now a dependency
• Some metadata header retrieval functions have been removed in favour of optics
• MeterSignature - Tuple Int Int replaced by
  TimeSignature - { numerator:: Int, denominator:: Int }
• MIDI pitch translation for B# and B## has been corrected
• Decorations can now be applied to chords and tuplets
• Chord symbols appear in the ADT as simple strings (without framing double quotes)
• The Metadata module has been renamed as Utils and many functions moved
  to modules named after the appropriate header