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/fs/rclone.go

@@ -1,14 +1,14 @@
 package fs
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "rclone",
 		Description: "Only list directories",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "about", Description: "Get quota information from the remote"},
 			{Name: "authorize", Description: "Remote authorization"},
 			{Name: "backend", Description: "Run a backend specific command"},
@@ -60,7 +60,7 @@ func init() {
 			{Name: "size", Description: "Prints the total size and number of objects in remote:path"},
 			{Name: "sync", Description: "Make source and dest identical, modifying destination only"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--dirs-only", Description: "Only list directories"},
 			{Name: "--files-only", Description: "Only list files"},
 			{Name: "--recursive", Description: "Recurse into the listing"},