Add conversions between DataBits, StopBits and their numeric representation #329

Job	Run time
cargo-deny (advisories)	20s
lint	52s
cargo-deny (bans licenses sources)	16s
aarch64-apple-ios / build	47s
aarch64-apple-darwin / build	51s
aarch64-unknown-linux-gnu / build	32s
aarch64-unknown-linux-musl / build	50s
armv7-linux-androideabi / build	32s
i686-pc-windows-gnu / build	2m 38s
arm-linux-androideabi / build	20s
i686-pc-windows-msvc / build	2m 11s
i686-unknown-linux-gnu / build	47s
msrv-aarch64-apple-darwin / build	47s
i686-unknown-linux-musl / build	49s
msrv-arm-linux-androideabi / build	41s
msrv-x86_64-pc-windows-msvc / build	1m 16s
msrv-x86_64-unknown-freebsd / build	45s
msrv-x86_64-unknown-linux-gnu / build	33s
msrv-x86_64-unknown-linux-musl / build	54s
msrv-x86_64-unknown-netbsd / build	40s
x86_64-apple-darwin / build	1m 4s
x86_64-pc-windows-gnu / build	1m 27s
x86_64-pc-windows-msvc / build	2m 9s
x86_64-unknown-freebsd / build	22s
x86_64-unknown-linux-gnu / build	43s
x86_64-unknown-linux-musl / build	51s
x86_64-unknown-netbsd / build	34s
	24m 31s

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