Adding support for TLS DOCKER_HOST

Workarounds courtesy of
https://github.com/fsouza/go-dockerclient/issues/173. They can likely be
removed after better support for TLS docker connections is added to
go-dockerclient.
Only verify TLS via CA if DOCKER_TLS_VERIFY is set
Merge remote-tracking branch 'origin/master' into add-tls-support

Conflicts:
	Deps
Allowing host scheme to be overwritten by env var
Adding documentation about TLS-related env vars
Bump version in README in anticipation of release
Merge pull request #147 from rafecolton/add-tls-support

Add TLS support