Improve Font::layout lifetime bounds

Closes #151

See merge request !156

Update ttf-parser to 0.6

Closes #149

See merge request !155

Update kerning logic

* Add single_ttf, single_otf benches.
* Adjust thrashing size to new fonts.

This show the poorer performance of rusttype's handling of otfs 
currently compared to ttfs.

Use owned_ttf_parser crate

See merge request !154

Push unsafety out of rusttype to the very specific usage in the
dependency.

Implement Support for building outlines

See merge request !153

This brings back support for building outlines, which disappeared in
rusttype 0.9.

Exo2 ttf vs otf

See merge request !152

Support .otf fonts by switching to ttf-parser & ab_glyph_rasterizer

Closes #137

See merge request !151

* Rename "rusttype-dev" private crate "dev"

Update changelog

* Add Exo2-Light.oft refrence tests & benchmark.
* Update readme.
* Remove crate rasterization logic.
* Update render references (byte differences, visually the same).

Implement Default for the geometry structs

See merge request !150

Remove arrayvec dependency

Closes #146

See merge request !149

cargo fmt