improve command handling, change argument/option registration

README.md

@@ -28,20 +28,20 @@ dependencies {
 ## Usage
 
 ```kotlin
-fun main(args: Array<String>) = cli("application") {
+fun main(args: Array<String>) = command("application") {
     execute {
         // define execution of command (e.g., display help)
         help()
     }
 
-    // declare command "greet"
-    command("greet") {
-        // declare arguments
-        val speakersArg by argument.string("speakers").variable(min = 1)
+    // register command "greet"
+    +command("greet") {
+        // declare and register arguments
+        val speakersArg = +argument.string("speakers").variable(min = 1)
 
-        // declare options
-        val greetingOpt by option.string("greeting", "greet", "g").orElse("Hello")
-        val nameOpt by option.string("name", "n").orNull()
+        // declare and register options
+        val greetingOpt = +option.string("greeting", "greet", "g").orElse("Hello")
+        val nameOpt = +option.string("name", "n").orNull()
 
         execute {
             // retrieve the arguments and options
@@ -52,11 +52,11 @@ fun main(args: Array<String>) = cli("application") {
             println("${speakers.joinToString()}: $greeting ${name ?: "World"}!")
         }
 
-        // declare more commands...
+        // register more commands...
     }
 
-    // declare fallback command
-    fallback.string("value") { valueArg ->
+    // register fallback command "value"
+    +command.fallback.string("value") { valueArg ->
         execute {
             // retrieve the value used for the fallback command
             val value by valueArg