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/ops/sqlite3.go

@@ -1,14 +1,14 @@
 package ops
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "sqlite3",
 		Description: "A command line interface for SQLite version 3",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-append", Description: "Append the database to the end of the file"},
 			{Name: "-ascii", Description: "Set output mode to 'ascii'"},
 			{Name: "-bail", Description: "Stop after hitting an error"},