feat: Add Draft 4 support

[Stranger6667]

• Docs update

[codecov]

Codecov Report

Merging #34 into master will increase coverage by 2.42%.
The diff coverage is 89.51%.

@@            Coverage Diff             @@
##           master      #34      +/-   ##
==========================================
+ Coverage   73.16%   75.59%   +2.42%     
==========================================
  Files          42       45       +3     
  Lines        2817     2917     +100     
==========================================
+ Hits         2061     2205     +144     
+ Misses        756      712      -44     

Impacted Files	Coverage Δ
src/keywords/mod.rs	100.00% <ø> (ø)
src/keywords/type_.rs	81.36% <ø> (ø)
src/keywords/legacy/type_draft_4.rs	84.41% <84.41%> (ø)
src/schemas.rs	48.01% <96.42%> (+26.75%)	⬆️
draft/src/lib.rs	100.00% <100.00%> (ø)
src/keywords/legacy/maximum_draft_4.rs	100.00% <100.00%> (ø)
src/keywords/legacy/minimum_draft_4.rs	100.00% <100.00%> (ø)
... and 1 more

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