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/kitty.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:        "kitty",
 		Description: "A cat like utility to display images in the terminal",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "close-tab", Description: "Close the specified tab(s)"},
 			{Name: "close-window", Description: "Close the specified window(s)"},
 			{Name: "detach-tab", Description: "Detach the specified tab"},
@@ -21,7 +21,7 @@ func init() {
 			{Name: "set-window-title", Description: "Set the title of the specified window(s)"},
 			{Name: "signal-child", Description: "Send one or more signals to the foreground process in the specified window(s)"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--align", Description: "Horizontal alignment for the displayed image"},
 			{Name: "--place", Description: "Choose where on the screen to display the image"},
 			{Name: "--scale-up", Description: "Mirror the image about a horizontal or vertical axis or both"},