Added top level .Hugo variable with version, commit and generator information + docs

Added Version, CommitHash and BuildDate to hugolib/hugo.go and used it in build
Removed commitHash and buildDate from commands/version.go and used hugolib vars
Removed getDateFormat function from commands/version.go

Conflicts:
	README.md
	docs/content/templates/variables.md

hugolib/node.go

@@ -29,6 +29,7 @@ type Node struct {
 	Params      map[string]interface{}
 	Date        time.Time
 	Sitemap     Sitemap
+	Hugo        *HugoInfo
 	UrlPath
 }