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/view/xed.go

@@ -1,14 +1,14 @@
 package view
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "xed",
 		Description: "Xcode text editor invocation tool",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--launch", Description: "Launches Xcode, opening a new empty unsaved file"},
 			{Name: "--create", Description: "Selects the given line in the last file opened"},
 			{Name: "--background", Description: "Opens Xcode without activating it; the process that invoked xed remains in front"},