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/gum.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:        "gum",
 		Description: "Background Color",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "choose", Description: "Choose an option from a list of choices"},
 			{Name: "confirm", Description: "Ask a user to confirm an action"},
 			{Name: "prompt", Description: "Prompt to display"},
@@ -27,7 +27,7 @@ func init() {
 			{Name: "pager", Description: "Scroll through a file"},
 			{Name: "content", Description: "Display content to scroll"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--background", Description: "Background Color"},
 			{Name: "--foreground", Description: "Foreground Color"},
 			{Name: "--border", Description: "Border Style"},