Keeping the license as part of every file bloats up the files
unnecessarily and introduces an additional overhead to the creation of
new modules.

Since cargo already provides excellent dependency management, most of
the code-reuse of Alacritty should occur through Rust's dependency
management instead of copying it source.

If code is copied partially, copying the license from the main license
file should be just as easy as copying from the top of the file and
making some adjustments based on where it is used is likely necessary
anyways.

Fixes #1754.

This resolves an issue with the selection clamping, where no selection
would be rendered at all when the start was above the viewport while the
end was below it.

Fixes regression introduced in 6b327b6f8f0f308ff8f46cdf551ce0d0f3eda60b.

Fixes #3355.

Fixes resize regression from 15cc07c069b09f109ed18fb94e02e9650be7fa33.

Fixes #3257.

Previous implementation was querying Fontconfig using `charset` in a pattern,
which was leading to unpredictable fallbacks in some cases, since Fontconfig
was picking the font with the most coverage for a given charset, regardless of
user configuration. Moreover all fallback was based on font_match which is
extremely slow for such performance sensitive task as a fallback, so alacritty
had a hard times on vtebench's unicode-random-write.

The new approach is to use some internal fallback list from font_sort
and iterate over it to get a proper fallback font, since it matches the
following example query from `fc-match`:

`fc-match -s "monospace:pixelsize=X:style=Y"

That being said it's more intuitive for users to setup their system Fontconfig
fallback, and also most applications are doing similar things. Moreover the new
implementation uses internal caches over Fontconfig API when possible and
performs font matches only once during load of requested font with font_sort,
which leads to dramatically improved performance on already mentioned
vtebench's unicode-random-write.

Fixes #3176.
Fixes #3134.
Fixes #2657.
Fixes #1560.
Fixes #965.
Fixes #511.