Fix NLL migration warning

See merge request !147

Change urls to redox-os org

Fix missing glyph errors in gpu_cache and add benchmarks

Fix `rect_for` searches failing to find cached glyphs
Fix `cache_queued` unsound tracking of in use rows

Attempt at fixing rasterize returning negative values

Use `position` instead of `pixel_bounding_box` for width calculation in example

docs.rs

Upgrade to latest linked-hash-map

Delete non-free asset

Derive Debug for many structs

This is probably not the ideal solution for the bug here, but I do not know enough about what's happening to come up with a better one.

Fixes #37.

This respects trailing whitespace. With the previous method, concatenating “Hello ” and “World!” yielded “HelloWorld!”.