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/jvm/keytool.go

@@ -1,14 +1,14 @@
 package jvm
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "keytool",
 		Description: "Show help message",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-h", Description: "Show help message"},
 			{Name: "-v", Description: "Verbose output"},
 			{Name: "-alias", Description: "Alias name of the entry to process"},