Make ReadBuf::new public #2347

Job	Run time
Verify hyper.h is up to date	17s
Check Style	5s
Test C API (FFI)	14s
minimal-versions	23s
Test with Miri	1m 4s
features	20s
Check MSRV	26s
Test stable on ubuntu-latest	1m 11s
udeps	30s
Test stable on windows-latest	3m 46s
Test stable on macOS-latest	1m 51s
Test beta on ubuntu-latest	1m 14s
Test beta on windows-latest	1m 57s
Test beta on macOS-latest	1m 47s
Test nightly on ubuntu-latest	1m 33s
Test nightly on windows-latest	2m 30s
Test nightly on macOS-latest	2m 42s
Check exposed types	38s
Build docs	28s
CI is green	1s
	22m 57s

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