Update README with more info about logo size
Fix bug where weird white block could appear at bottom of page.

This bug occured if the final code sample extended beyond the
explanation at the bottom of the page.

To fix it, I simply made the background color of body a soft
blue.
Add note to README about variables.scss
Add asides for nice-looking notes and warnings

You can now use <aside> with the classes

- warning
- success
- notice

to add little colored notes to your API docs! Examples are in
source/index.md.

Also, note that if you have a custom variables.scss, you'll have
to add

+$aside-notice-bg: #8fbcd4;
+$aside-warning-bg: #c97a7e;
+$aside-success-bg: #6ac174;

to it.