Feature docker getversion

Small (low prio) function to query the docker version info, return something like this:
(
    [ApiVersion] => 1.15
    [Arch] => amd64
    [GitCommit] => 4e9bbfa
    [GoVersion] => go1.3.3
    [KernelVersion] => 3.13.0-39-generic
    [Os] => linux
    [Version] => 1.3.1
)
One could stpore the api version in the docker object and use it for compatibility decisions later. e.g. give an err if the api is less that a version tested with docker-php