fretwork v0.9

DRUMS!

Drums now works through the entire pipeline, keeps the fast performance from last update

Build - caches everything it needs (recommend a rebuild, since roll spans are required)
Analyze - Adds a new tab to the sheet (1 row per song includes both 1x/2x kick versions), and allows for drum diff write back for game use
Render - Renders all 3 H+T+K metrics for drums, and stacks 1x and 2x on the same graph for songs that have it

Readme & Methodology updated to include the specifics and formula details