Added `Flock` object for automatic unlock on drop. #115

Job	Run time
macos	1m 26s
linux_native_builds (x86_64-unknown-linux-gnu)	1m 8s
minver	12s
rust_stable	1m 1s
linux_native_builds (x86_64-unknown-linux-musl)	1m 4s
rustfmt	13s
tier3 (x86_64-unknown-dragonfly)	56s
tier3 (x86_64-unknown-openbsd)	50s
tier3 (armv7-unknown-linux-uclibceabihf)	1m 0s
tier3 (x86_64-unknown-haiku)	59s
redox	38s
cross (arm-unknown-linux-gnueabi)	1m 37s
cross_compiling (aarch64-linux-android)	33s
cross (armv7-unknown-linux-gnueabihf)	1m 27s
cross_compiling (arm-linux-androideabi)	36s
cross (i686-unknown-linux-gnu)	1m 27s
cross_compiling (armv7-linux-androideabi)	36s
cross (i686-unknown-linux-musl)	1m 39s
cross_compiling (i686-linux-android)	33s
cross (mips-unknown-linux-gnu)	1m 37s
cross_compiling (x86_64-linux-android)	31s
cross (mips64-unknown-linux-gnuabi64)	1m 37s
cross_compiling (arm-unknown-linux-musleabi)	33s
cross (mips64el-unknown-linux-gnuabi64)	1m 37s
cross_compiling (x86_64-unknown-fuchsia)	30s
cross (mipsel-unknown-linux-gnu)	1m 30s
cross_compiling (x86_64-unknown-illumos)	24s
cross (powerpc64le-unknown-linux-gnu)	1m 37s
cross_compiling (aarch64-apple-ios, true)	27s
cross_compiling (powerpc64-unknown-linux-gnu)	2m 16s
cross_compiling (s390x-unknown-linux-gnu)	34s
cross_compiling (x86_64-unknown-linux-gnux32)	34s
cross_compiling (x86_64-unknown-netbsd)	28s
	32m 10s

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