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/jest.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:        "jest",
 		Description: "A delightful JavaScript Testing Framework with a focus on simplicity",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--bail", Description: "Whether to use the cache"},
 			{Name: "--no-cache", Description: "Whether to use the cache"},
 			{Name: "--changedFilesWithAncestor", Description: "Runs tests related to the changes since the provided branch or commit hash"},