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/ops/nvm.go

@@ -1,14 +1,14 @@
 package ops
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "nvm",
 		Description: "Node version",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "uninstall", Description: "Uninstall a version"},
 			{Name: "use", Description: "Modify PATH to use <version>. Uses .nvmrc if available and version is omitted"},
 			{Name: "exec", Description: "Run <command> on <version>. Uses .nvmrc if available and version is omitted"},
@@ -25,7 +25,7 @@ func init() {
 			{Name: "dir", Description: "Display path to the cache directory for nvm"},
 			{Name: "clear", Description: "Empty cache directory for nvm"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--no-colors", Description: "Suppress colored output"},
 			{Name: "--no-alias", Description: "Suppress `nvm alias` output"},
 			{Name: "--silent", Description: "Silences stdout/stderr output"},