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/js/eslint.go

@@ -1,14 +1,14 @@
 package js
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "eslint",
 		Description: "Pluggable JavaScript linter",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--no-eslintrc", Description: "Disable use of configuration from .eslintrc.*"},
 			{Name: "-c", Description: "Use this configuration, overriding .eslintrc.* config options if present"},
 			{Name: "--env", Description: "Specify environments"},