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/pytest.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:        "pytest",
 		Description: "Control assertion debugging tools.",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--assert", Description: "Remove all cache contents at start of test run"},
 			{Name: "--cache-show", Description: "Per-test capturing method"},
 			{Name: "--code-highlight", Description: "Whether code should be highlighted (only if --color is also enabled)"},