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/sys/vultr_cli.go

@@ -1,14 +1,14 @@
 package sys
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "vultr-cli",
 		Description: "Bare Metal ID",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "account", Description: "Retrieve information about your account"},
 			{Name: "apps", Description: "Display all available applications"},
 			{Name: "list", Description: "List applications"},
@@ -60,7 +60,7 @@ func init() {
 			{Name: "script", Description: "Startup script commands"},
 			{Name: "snapshot", Description: "Snapshot commands"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--os", Description: "ID of the operating system that will be installed on the server"},
 			{Name: "--persistent_pxe", Description: "Enable persistent_pxe"},
 			{Name: "--plan", Description: "ID of the plan that the server will subscribe to"},