Use i8 positions in compound glyphs

Closes #18

See merge request !25

Safe rework of get_glyph_shape

Closes #15 and #16

See merge request !24

Remove unsafe usages
Don't use Vertex data for 2 different thigns
Simplify type usages

Fix/address clippy lints

See merge request !23

cargo fmt + remove commented code

See merge request !22

Optimise get_v_metrics, scale_for_pixel_height

See merge request !21

Optimise get_glyph_h_metrics

See merge request !20

3.5x faster benchmarks

Optimise get_glyph_box

See merge request !19

Optimise find_glyph_index (format=12,13)

See merge request !18

benchmarks 2x faster

deja vu benchmark 1.4x faster

Add benchmark regression tests & gitlab-ci

See merge request !17

Added units_per_em function

Update links to point to redox-os repository