[host]: add not implemented methods.

Merge pull request shirou#382 from acd/master

Only read /proc/stat once when cpu.Times(true) is called on Linux

Merge pull request shirou#379 from magiconair/fix-host-boottime-race

Fix data race in host.BootTime

Merge pull request shirou#358 from ablagoev/optimize-net-connections

Fromat socketType properly in tcp duplication check key

[host]darwin: PlatformInformation has been 5 values other is 4.

Merge pull request shirou#320 from tychoish/close-files-more-often

close open files

Merge pull request shirou#307 from shirou/freebsd_cpu_cores_num

[cpu]freebsd: cpu.Info() now returns CPUInfos same number as CPU nums.

Merge pull request shirou#293 from HeChuanXUPT/patch-1

fix: division by zero possible

Add OpenBSD to README (Thank you @mpfz0r)