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/ant.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:        "ant",
 		Description: "Apache Ant - Java library and command-line build tool",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--help", Description: "Show help for ant"},
 			{Name: "--noconfig", Description: "Enable use of jikes by default, unless set explicitly in configuration files"},
 			{Name: "--execdebug", Description: "Print ant exec line generated by this launch script"},