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_pack.go

@@ -1,18 +1,18 @@
 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-pack",
 		Description: "Build an npm package",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "help", Description: "Prints this message or the help of the given subcommand(s)"},
 			{Name: "test", Description: "Run tests for WebAssembly module"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--help", Description: "Show help for wasm-pack or for the given subcommand(s)"},
 			{Name: "--quiet", Description: "Suppress output from stdout"},
 			{Name: "--version", Description: "Show version for wasm-pack"},