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/dog.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:        "dog",
 		Description: "Human-readable host names, nameservers, types, or classes",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "A", Description: "Query Domain A Record"},
 			{Name: "MX", Description: "Query Domain MX Record"},
 			{Name: "CNAME", Description: "Query Domain CNAME Record"},
@@ -18,7 +18,7 @@ func init() {
 			{Name: "TTL", Description: "Query TTL Record"},
 			{Name: "ANY +noall +answer", Description: "Query ALL DNS Records"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-q", Description: "Host name or IP address to query"},
 			{Name: "-t", Description: "Type of the DNS record being queried (A, MX, NS...)"},
 			{Name: "-n", Description: "Address of the nameserver to send packets to"},