Improve documentation, add examples #57

Job	Run time
Doc	19s
Clippy	18s
Features /	15s
Cross / i686-unknown-linux-gnu	1m 9s
Features / simdutf8 uuid-1	15s
Format	11s
Cross / i586-unknown-linux-gnu	1m 10s
Miri /	41s
Cross / armv7-unknown-linux-gnueabihf	1m 13s
Test / x86_64-pc-windows-msvc	57s
Cross / aarch64-unknown-linux-gnu	1m 11s
Miri / --release	41s
Toolchain / stable	18s
Test / x86_64-pc-windows-msvc --release	57s
Cross / thumbv6m-none-eabi	1m 18s
Toolchain / stable --release	16s
Toolchain / beta	14s
Toolchain / beta --release	15s
Toolchain / nightly	16s
Toolchain / nightly --release	17s
	12m 11s

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