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/golang/goctl.go

@@ -1,14 +1,14 @@
 package golang
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "goctl",
 		Description: "A cli tool to generate go-zero code",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "api", Description: "Generate api related files"},
 			{Name: "dart", Description: "Generate dart files for provided api in api file"},
 			{Name: "doc", Description: "Generate doc files"},
@@ -50,7 +50,7 @@ func init() {
 			{Name: "upgrade", Description: "Upgrade goctl to latest version"},
 			{Name: "help", Description: "Help about any command"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--api", Description: "The api file"},
 			{Name: "--dir", Description: "The target dir"},
 			{Name: "--hostname", Description: "Hostname of the server"},