[doc][s]: document validate command (been around for a while).
[validate][xs]: dpm validate .../datapackage.json now works.

* Used to expect only path to data package and would barf if passed path to datapackage.json.
[deps][s]: remove obsolete external lib dependencies.
[package.json][s]: switch author and primary repo.
[package.json][s]: bump version to 0.6.0 and increase datapackage-validate dep.
Merge branch 'master' of github.com:okfn/dpm