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/pipx.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:        "pipx",
 		Description: "Installed package",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "install", Description: "Install a package"},
 			{Name: "package_spec", Description: "Package name or pip installation spec"},
 			{Name: "inject", Description: "Installs packages to an existing pipx-managed virtual environment"},
@@ -24,7 +24,7 @@ func init() {
 			{Name: "environment", Description: "Print a list of variables used in pipx.constants"},
 			{Name: "completions", Description: "Print instructions on enabling shell completions for pipx"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--include-deps", Description: "Include apps of dependent packages"},
 			{Name: "--force", Description: "Modify existing virtual environment and files in PIPX_BIN_DIR"},
 			{Name: "--suffix", Description: "Optional suffix for virtual environment and executable names"},