gm 2.0.0 New Components

Features

• Add many new components (#11 #4).
• Represent music with data frames.
• Refactor code. Now it's more developer-friendly.
• Reduce package dependencies.

Breaking Changes

• Deprecate argument tie of Line(). Use Tie() instead.
• Deprecate argument unit of Tempo(). Use marking instead.
• Change arguments of export().
• Remove tuplet() and Tupler(). Use argument durations of Line() instead.