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/gatsby.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:        "gatsby",
 		Description: "Set host. Defaults to localhost",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "develop", Description: "Start the Gatsby development server"},
 			{Name: "build", Description: "Compile your application and make it ready for deployment"},
 			{Name: "serve", Description: "Serve the production build of your site for testing"},
@@ -18,7 +18,7 @@ func init() {
 			{Name: "docs", Description: "Documentation about using and creating plugins"},
 			{Name: "repl", Description: "Gatsby will prompt you to type in commands and explore"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-H", Description: "Set host. Defaults to localhost"},
 			{Name: "-p", Description: "Set port. Defaults to env.PORT or 8000"},
 			{Name: "-o", Description: "Open the site in your (default) browser for you"},