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/ssh_keygen.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:        "ssh-keygen",
 		Description: "Generates, manages and converts authentication keys for ssh",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-A", Description: "When saving a private key, this option specifies the number of KDF"},
 			{Name: "-B", Description: "Show the bubblebabble digest of specified private or public key file"},
 			{Name: "-b", Description: "Specifies the number of bits in the key to create"},