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/jvm/gradle.go

@@ -1,14 +1,14 @@
 package jvm
 
 import (
-	"github.com/versenilvis/iris/commands/core"
+	"github.com/versenilvis/iris/spec"
 )
 
 func init() {
-	core.Register(&core.Spec{
+	spec.Register(&spec.Spec{
 		Name:        "gradle",
 		Description: "Log all warnings",
-		Subcommands: []core.Subcommand{
+		Subcommands: []spec.Subcommand{
 			{Name: "build", Description: "Compute all outputs"},
 			{Name: "run", Description: "Run applications"},
 			{Name: "check", Description: "Run all checks"},
@@ -21,7 +21,7 @@ func init() {
 			{Name: "init", Description: "Create new Gradle builds, with new or existing projects"},
 			{Name: "test", Description: "Run a test task"},
 		},
-		Options: []core.Option{
+		Options: []spec.Option{
 			{Name: "-?", Description: "Shows a help message with all available CLI options"},
 			{Name: "-v", Description: "Prints Gradle, Groovy, Ant, JVM, and operating system version information"},
 			{Name: "-S", Description: "Print out the full (very verbose) stacktrace for any exceptions"},