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/jvm/dart.go

@@ -1,14 +1,14 @@
 package jvm
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "dart",
 		Description: "The Dart file containing the main function",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "analyze", Description: "Analyze Dart code in a directory"},
 			{Name: "directory", Description: "Dart project directory to analyze"},
 			{Name: "compile", Description: "Compile Dart to various formats"},
@@ -60,7 +60,7 @@ func init() {
 			{Name: "non-nullable", Description: "Non-nullable by default. (no-op - on by default)"},
 			{Name: "triple-shift", Description: "Triple-shift operator"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--offline", Description: "Use cached packages instead of accessing the network"},
 			{Name: "--no-offline", Description: "Do not use cached packages instead of accessing the network"},
 			{Name: "-n", Description: "Report what dependencies would change but don't change any"},