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/st2.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:        "st2",
 		Description: "Show this help and exit",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "list", Description: "Get the list of actions"},
 			{Name: "get", Description: "Get individual action"},
 			{Name: "create", Description: "Create a new action"},
@@ -18,7 +18,7 @@ func init() {
 			{Name: "disable", Description: "Disable an existing action"},
 			{Name: "execute", Description: "Invoke an action manually"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-h", Description: "Show this help and exit"},
 			{Name: "-t", Description: "Print output in JSON format"},
 			{Name: "-y", Description: "Print output in YAML format"},