refactor(commands): separate commands and its core into two folders (#32)

- I think it would be better if one for commands only, one for the spec
handling core logic so people won't be confused by the core logic inside
the commands folder (cleaner I guess)
- Regen docs

commands/ops/gcloud.go

@@ -1,14 +1,14 @@
 package ops
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "gcloud",
 		Description: "Manage Google Cloud Platform resources and developer workflow",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "access-context-manager", Description: "Manage Access Context Manager resources"},
 			{Name: "active-directory", Description: "Manage Managed Microsoft AD resources"},
 			{Name: "ai-platform", Description: "Manage AI Platform jobs and models"},