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/rust/wasm_bindgen.go

@@ -1,14 +1,14 @@
 package rust
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "wasm-bindgen",
 		Description: "Generate bindings between WebAssembly and JavaScript",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--help", Description: "Show help for wasm-bindgen"},
 			{Name: "--version", Description: "Show version for wasm-bindgen"},
 			{Name: "--out-dir", Description: "Output directory"},