store notebook in `./book/figures/` and rest of files in `./book/book/figures/`

**note** a video was made to illustrate gradient fill. stored in robert's dropbox for now

- figures created in cover ipynb
  - make axes and fig transparent
  - export without background in savefig
- created doc in inkscape, set size to 210mmx210mm per OIT requirements
- OIT requires 210mmx210mm and at least 300 pixels, which is 36 dpi or 36x36 dpi
- Default inkscape was 96 dpi, which is 794x794 pixels
- import svg's to inkscape
- position figures
- apply gradient to lines
- delete three points
- export to png (default 96dpi is 100KB)
- export cover_small.png (45 dpi is 35KB) >>> for book logo