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/runner/rvm.go

@@ -1,14 +1,14 @@
 package runner
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "rvm",
 		Description: "Show version of rvm",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "use", Description: "Setup current shell to use a specific ruby version"},
 			{Name: "reset", Description: "Remove default and current settings, exit the shell"},
 			{Name: "info", Description: "Show information about the current ruby environment"},
@@ -23,7 +23,7 @@ func init() {
 			{Name: "uninstall", Description: "Uninstall one or many ruby versions, leaves their sources"},
 			{Name: "remove", Description: "Remove one or many ruby versions, including their sources"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--version", Description: "Show version of rvm"},
 			{Name: "--default", Description: "When used with ruby selection, sets a default ruby for new shells"},
 			{Name: "--debug", Description: "Enable debug mode"},