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/phpunit.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:        "phpunit",
 		Description: "Generate code coverage report in Clover XML format,",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--coverage-clover", Description: "Generate code coverage report in Clover XML format,"},
 			{Name: "--coverage-crap4j", Description: "Generate code coverage report in Crap4J XML format"},
 			{Name: "--coverage-html", Description: "Generate code coverage report in HTML format"},