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/ignite_cli.go

@@ -1,20 +1,20 @@
 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:        "ignite-cli",
 		Description: "Output usage information",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "new", Description: "Create a new React Native app"},
 			{Name: "g", Description: "Generate components and other app features"},
 			{Name: "update", Description: "Update installed generators"},
 			{Name: "doctor", Description: "Check your environment & display versions of installed dependencies"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-h", Description: "Output usage information"},
 			{Name: "-v", Description: "Output the version number"},
 			{Name: "--expo", Description: "Use Expo"},