Merge support for opening a connection from existing streams #98

Job	Run time
rustfmt_check	14s
build (ubuntu-latest, stable, default)	43s
build (ubuntu-latest, stable, sync,tls-rustls)	51s
build (ubuntu-latest, nightly, default)	40s
build (ubuntu-latest, nightly, sync,tls-rustls)	46s
build (windows-2019, stable, default)	1m 32s
build (windows-2019, stable, sync,tls-rustls)	2m 16s
build (windows-2019, nightly, default)	1m 24s
build (windows-2019, nightly, sync,tls-rustls)	1m 56s
build (macOS-latest, stable, default)	41s
build (macOS-latest, stable, sync,tls-rustls)	48s
build (macOS-latest, nightly, default)	38s
build (macOS-latest, nightly, sync,tls-rustls)	51s
	13m 20s

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