Bump version to 0.12 #121

Job	Run time
build (windows-latest, stable, build)	1m 20s
build (windows-latest, stable, test)	5m 31s
build (windows-latest, stable, clippy)	1m 50s
build (windows-latest, nightly, build)	59s
build (windows-latest, nightly, test)	4m 33s
build (windows-latest, nightly, clippy)	1m 34s
build (ubuntu-latest, stable, build)	48s
build (ubuntu-latest, stable, test)	2m 27s
build (ubuntu-latest, stable, clippy)	33s
build (ubuntu-latest, nightly, build)	41s
build (ubuntu-latest, nightly, test)	1m 58s
build (ubuntu-latest, nightly, clippy)	54s
build (macos-latest, stable, build)	34s
build (macos-latest, stable, test)	2m 20s
build (macos-latest, stable, clippy)	24s
build (macos-latest, nightly, build)	25s
build (macos-latest, nightly, test)	1m 51s
build (macos-latest, nightly, clippy)	47s
	29m 29s

Provide feedback