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/python/mamba.go

@@ -1,14 +1,14 @@
 package python
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "mamba",
 		Description: "Mamba is a fast, robust, and cross-platform package manager",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "activate", Description: "Activate an environment"},
 			{Name: "deactivate", Description: "Deactivate an environment"},
 			{Name: "clean", Description: "Remove unused packages and caches"},
@@ -37,7 +37,7 @@ func init() {
 			{Name: "xtl", Description: "List packages that require xtl package"},
 			{Name: "env", Description: "Manage environments"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-n", Description: "Name of environment"},
 			{Name: "-p", Description: "Full path to environment location (i.e. prefix)"},
 			{Name: "--file", Description: "Use locally built packages. Identical to '-c local'"},