Add conversions between DataBits, StopBits and their numeric representation #327

Job	Run time
lint	18s
cargo-deny (advisories)	16s
cargo-deny (bans licenses sources)	16s
aarch64-apple-darwin / build	1m 55s
aarch64-unknown-linux-gnu / build	34s
aarch64-apple-ios / build	1m 50s
aarch64-unknown-linux-musl / build	1m 22s
arm-linux-androideabi / build	35s
armv7-linux-androideabi / build	34s
i686-pc-windows-gnu / build	2m 40s
i686-pc-windows-msvc / build	2m 40s
i686-unknown-linux-gnu / build	55s
i686-unknown-linux-musl / build	1m 26s
msrv-aarch64-apple-darwin / build	3m 45s
msrv-arm-linux-androideabi / build	3m 35s
msrv-x86_64-pc-windows-msvc / build	5m 40s
msrv-x86_64-unknown-freebsd / build	3m 38s
msrv-x86_64-unknown-linux-gnu / build	3m 46s
msrv-x86_64-unknown-linux-musl / build	3m 40s
msrv-x86_64-unknown-netbsd / build	3m 39s
x86_64-apple-darwin / build	1m 38s
x86_64-pc-windows-gnu / build	4m 41s
x86_64-pc-windows-msvc / build	4m 40s
x86_64-unknown-freebsd / build	24s
x86_64-unknown-linux-gnu / build	1m 2s
x86_64-unknown-linux-musl / build	46s
x86_64-unknown-netbsd / build	26s
	56m 41s

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