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/pipenv.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:        "pipenv",
 		Description: "Python package manager",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "clean", Description: "Uninstalls all packages not specified in Pipfile.lock"},
 			{Name: "graph", Description: "Displays currently-installed dependency graph information"},
 			{Name: "install", Description: "Initializes a package manager or installs all packages from Pipfile"},
@@ -23,7 +23,7 @@ func init() {
 			{Name: "uninstall", Description: "Uninstalls a provided package and removes it from Pipfile"},
 			{Name: "update", Description: "Runs lock, then sync"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--unused", Description: "Given a code path, show potentially unused dependencies"},
 			{Name: "--db", Description: "Ignore specified vulnerability during PyUp Safety checks"},
 			{Name: "--output", Description: "Translates to --json, --full-report or --bare from PyUp Safety check"},