Add year-over-year stats plots

[smartflutist661]

Plot year-over-year statistics in appropriate formats.

[smartflutist661]

• [x] Total books read
• [x] Total authors read
• [x] Total cards
• [x] Total misspellings
• [x] Total hard mode squares
• [x] Total hero mode cards
• [x] Total participants

[smartflutist661]

Some tweaks to plots needed, but this is effectively complete