Prepare for v0.4.0 release #2084

Job	Run time
Test Suite [default features]	1m 58s
Test Suite [no features]	1m 58s
MSRV Build [Rust 1.65]	3m 1s
Test Suite [default except content_size]	1m 59s
Test Suite [default + serde]	2m 0s
Test Suite [std + flexbox]	1m 56s
Test Suite [std (no algorithms)]	2m 12s
Build Benchmarks	43s
Build Benchmarks (w/ yoga)	1m 20s
Clippy	30s
Documentation	13s
Rustfmt	19s
Markdown Lint	7s
Test Fixture Formatting	26s
Test Suite [alloc + all algorithms]	2m 4s
Test Suite [std + block)]	1m 56s
Test Suite [std + grid]	1m 55s
Test Suite [alloc + no algorithms]	2m 4s
	26m 41s

Provide feedback