Added `Flock` object for automatic unlock on drop. #136

Job	Run time
macos	1m 34s
rust_stable	1m 6s
linux_native_builds (x86_64-unknown-linux-gnu)	1m 6s
tier3 (x86_64-unknown-dragonfly)	55s
linux_native_builds (x86_64-unknown-linux-musl)	59s
tier3 (x86_64-unknown-openbsd)	55s
minver	13s
rustfmt	11s
tier3 (armv7-unknown-linux-uclibceabihf)	27s
tier3 (x86_64-unknown-haiku)	53s
redox	36s
cross_compiling (aarch64-linux-android)	35s
cross (arm-unknown-linux-gnueabi)	1m 31s
cross_compiling (arm-linux-androideabi)	1m 11s
cross (armv7-unknown-linux-gnueabihf)	1m 34s
cross_compiling (armv7-linux-androideabi)	32s
cross (i686-unknown-linux-gnu)	1m 40s
cross_compiling (i686-linux-android)	1m 6s
cross (i686-unknown-linux-musl)	1m 40s
cross_compiling (x86_64-linux-android)	35s
cross (mips-unknown-linux-gnu)	1m 40s
cross_compiling (arm-unknown-linux-musleabi)	35s
cross (mips64-unknown-linux-gnuabi64)	1m 44s
cross_compiling (x86_64-unknown-fuchsia)	14s
cross (mips64el-unknown-linux-gnuabi64)	1m 40s
cross_compiling (x86_64-unknown-illumos)	13s
cross (mipsel-unknown-linux-gnu)	1m 34s
cross_compiling (aarch64-apple-ios, true)	22s
cross (powerpc64le-unknown-linux-gnu)	1m 37s
cross_compiling (powerpc64-unknown-linux-gnu)	31s
cross_compiling (s390x-unknown-linux-gnu)	34s
cross_compiling (x86_64-unknown-linux-gnux32)	14s
cross_compiling (x86_64-unknown-netbsd)	14s
	30m 31s

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