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/xcodes.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:        "xcodes",
 		Description: "Manage the Xcode versions installed on your Mac",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "download", Description: "Download a specific version of Xcode"},
 			{Name: "version", Description: "The version to install"},
 			{Name: "install", Description: "Download and install a specific version of Xcode"},
@@ -20,7 +20,7 @@ func init() {
 			{Name: "update", Description: "Update the list of available versions of Xcode"},
 			{Name: "signout", Description: "Clears the stored username and password"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--latest", Description: "Update and then install the latest non-prerelease version available"},
 			{Name: "--latest-prerelease", Description: "The path to an aria2 executable. Searches $PATH by default"},
 			{Name: "--no-aria2", Description: "Don't use aria2 to download Xcode, even if it's available"},