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/js/next.go

@@ -1,14 +1,14 @@
 package js
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "next",
 		Description: "A port number on which to start the application",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "build", Description: "Create an optimized production build of your application"},
 			{Name: "dev", Description: "Start the application in development mode"},
 			{Name: "start", Description: "Start the application in production mode"},
@@ -18,7 +18,7 @@ func init() {
 			{Name: "enable", Description: "Enable Next.js' telemetry collection"},
 			{Name: "disable", Description: "Disable Next.js' telemetry collection"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-p", Description: "A port number on which to start the application"},
 			{Name: "-H", Description: "Hostname on which to start the application"},
 			{Name: "-h", Description: "Output usage information"},