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/mongoimport.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:        "mongoimport",
 		Description: "Import data from a JSON, CSV, or TSV file into a MongoDB instance",
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--help", Description: "Returns information on the options and use of mongoimport"},
 			{Name: "--verbose", Description: "Runs mongoimport in a quiet mode that attempts to limit the amount of output"},
 			{Name: "--version", Description: "Returns the mongoimport release number"},