This commit adds support for Info(), BootTime() and Uptime() in package
Host. It uses no cgo, preferring to parse the output of `kstat -p`
instead.
Thanks go to @gfrey for the parsing logic for `/etc/release` and `uname`.
This enables using gopsutil in a codebase that gets built on other OSes
than the ones supported. Instead of a build failure as before, due to
the build tags, gopsutil will now throw an "not implemented" runtime
error.
Fixes#234.
WAKAYAMA Shirou