ast: default value support in generation

ast/src/main/ast/pork.yml

@@ -123,6 +123,7 @@ types:
       type: Symbol
     - name: multiple
       type: Boolean
+      defaultValue: "false"
   FunctionDefinition:
     parent: Definition
     values:

ast/src/main/kotlin/gay/pizza/pork/ast/ArgumentSpec.kt

@@ -6,4 +6,4 @@ import kotlinx.serialization.Serializable
 
 @Serializable
 @SerialName("argumentSpec")
-class ArgumentSpec(var symbol: Symbol, var multiple: Boolean)
+class ArgumentSpec(var symbol: Symbol, var multiple: Boolean = false)