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/stack.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:        "stack",
 		Description: "The Haskell Tool Stack",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "build", Description: "Build the package(s) in the current directory/configuration"},
 			{Name: "test", Description: "Shortcut for 'build --test'"},
 			{Name: "bench", Description: "Shortcut for 'build --bench'"},
@@ -25,7 +25,7 @@ func init() {
 			{Name: "dot", Description: "Visualize your project's dependency graph using Graphviz dot"},
 			{Name: "repl", Description: "Load a REPL"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "--help", Description: "Show help for stack"},
 			{Name: "--version", Description: "Show version for stack"},
 			{Name: "--numeric-version", Description: "Show only the numeric version for stack"},