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/hugo.go

@@ -0,0 +1,25 @@
+package hugolib
+
+const Version = "0.13-DEV"
+
+var (
+	CommitHash string
+	BuildDate  string
+)
+
+// Hugo contains all the information about the current Hugo environment
+type HugoInfo struct {
+	Version    string
+	Generator  string
+	CommitHash string
+	BuildDate  string
+}
+
+func NewHugoInfo() HugoInfo {
+	return HugoInfo{
+		Version:    Version,
+		CommitHash: CommitHash,
+		BuildDate:  BuildDate,
+		Generator:  `<meta name="generator" content="Hugo ` + Version + `" />`,
+	}
+}