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/sys/nextflow.go

@@ -1,14 +1,14 @@
 package sys
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "nextflow",
 		Description: "Session ID",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "clean", Description: "Clean up project cache and work directories (Default: last run)"},
 			{Name: "clone", Description: "Clone a project into a folder"},
 			{Name: "config", Description: "Print a project configuration"},
@@ -27,7 +27,7 @@ func init() {
 			{Name: "self-update", Description: "Update nextflow runtime to the latest available version"},
 			{Name: "view", Description: "View project script file(s)"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-after", Description: "Clean up runs executed after the specified one"},
 			{Name: "-before", Description: "Clean up runs executed before the specified one"},
 			{Name: "-but", Description: "Clean up all runs except the specified one"},