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/k6.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:        "k6",
 		Description: "Create an archive",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "archive", Description: "Create an archive"},
 			{Name: "cloud", Description: "Run a test on the cloud"},
 			{Name: "completion", Description: "Generate the autocompletion script for the specified shell"},
@@ -60,7 +60,7 @@ func init() {
 			{Name: "max", Description: "Max available virtual users"},
 			{Name: "stats", Description: "Show test metrics"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--address", Description: "Address of the API server"},
 			{Name: "--batch", Description: "Max parallel batch reqs (default 20)"},
 			{Name: "--batch-per-host", Description: "Max parallel batch reqs per host (default 6)"},