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/atuin.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:        "atuin",
 		Description: "Magical shell history",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "history", Description: "Manipulate shell history"},
 			{Name: "start", Description: "Begins a new command in the history"},
 			{Name: "end", Description: "Finishes a new command in the history (adds time, exit code)"},
@@ -28,7 +28,7 @@ func init() {
 			{Name: "uuid", Description: "Generate a UUID"},
 			{Name: "gen-completions", Description: "Generate shell completions"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--exit", Description: "List all items in history"},
 			{Name: "--cwd", Description: "Show only the text of the command"},
 			{Name: "--format", Description: "Get the last command ran"},