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/adb.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:        "adb",
 		Description: "Forward-lock the app",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "devices", Description: "List connected devices"},
 			{Name: "help", Description: "Show this help message"},
 			{Name: "get-state", Description: "Print offline | bootloader | device"},
@@ -60,7 +60,7 @@ func init() {
 			{Name: "install-multiple", Description: "Push multiple APKs to the device for a single package and install them"},
 			{Name: "install-multi-package", Description: "Push one or more packages to the device and install them atomically"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-l", Description: "Forward-lock the app"},
 			{Name: "-r", Description: "Replace existing application"},
 			{Name: "-t", Description: "Allow test packages"},