Move mux functionality into CondSwap chip #204

Job	Run time
Test on i686-unknown-linux-gnu	13m 34s
Test on i686-unknown-linux-gnu with beta features	14m 1s
Build target wasm32-unknown-unknown	1m 48s
Bitrot check	1m 34s
Build target wasm32-wasi	1m 38s
Test on i686-unknown-linux-gnu with nightly features	15m 38s
Book tests	1m 43s
Intra-doc links	1m 29s
Rustfmt	14s
Test on ubuntu-latest	7m 19s
Test on windows-latest	9m 30s
Test on macOS-latest	14m 32s
Test on ubuntu-latest with beta features	7m 12s
Test on windows-latest with beta features	9m 45s
Test on macOS-latest with beta features	16m 49s
Test on ubuntu-latest with nightly features	8m 20s
Test on windows-latest with nightly features	10m 56s
Test on macOS-latest with nightly features	20m 33s
	2h 36m 35s

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