Update README.md

Fix README typos.
Update rust-geom
Implement the beginnings of the box model for render boxes
Add NSPR and NSS submodules
Add NSS and NSPR to the build
Don't clip layers to the screen area
Clamp scrolling to the page boundaries
Stop hammering on the compositor
Fix corrupted textures when resizing.
Don't try to remove whitespace twice if it's the only node.

Fixes a failure on Wikipedia.
Color links blue
Add flows if requested to the display list info.

This will be used for hit testing.
base and bounds methods for DisplayItem
Basic hit testing functionality
Update rust-css and rust-netsurfcss
Add horizontal borders, margins and padding. Broken until rust-css supports padding
Fix method names and dynamic borrow check failures
Refactor a bit and compute vertical margins as well.
Update rust-css and fix some dynamic borrow check failures
Add comments and compute heights properly