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/whois.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:        "whois",
 		Description: "Query a database for information about a domain registrant",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-a", Description: "Use the American Registry for Internet Numbers (ARIN) database"},
 			{Name: "-A", Description: "Use the Asia/Pacific Network Information Center (APNIC) database"},
 			{Name: "-b", Description: "Use the Network Abuse Clearinghouse database"},