fix option type definition to match usage. (#1119)

* fix option type def

* add test
improve types

* change definition order

* change def order

* fix typing

* improve typing enforce current implementation

* final patch

* drop all void returning option

* fix missing boolean type for default value

* clean code

* clean code

typings/index.d.ts

@@ -159,17 +159,19 @@ declare namespace commander {
      *
      * @returns Command for chaining
      */
-    option(flags: string, description?: string, fn?: ((arg1: any, arg2: any) => void) | RegExp, defaultValue?: any): Command;
-    option(flags: string, description?: string, defaultValue?: any): Command;
+    option(flags: string, description?: string, defaultValue?: string | boolean): Command;
+    option(flags: string, description: string, regexp: RegExp, defaultValue?: string | boolean): Command;
+    option<T>(flags: string, description: string, fn: (value: string, previous: T) => T, defaultValue?: T): Command;
 
     /**
      * Define a required option, which must have a value after parsing. This usually means
      * the option must be specified on the command line. (Otherwise the same as .option().)
      *
      * The `flags` string should contain both the short and long flags, separated by comma, a pipe or space.
      */
-    requiredOption(flags: string, description?: string, fn?: ((arg1: any, arg2: any) => void) | RegExp, defaultValue?: any): Command;
-    requiredOption(flags: string, description?: string, defaultValue?: any): Command;
+    requiredOption(flags: string, description?: string, defaultValue?: string | boolean): Command;
+    requiredOption(flags: string, description: string, regexp: RegExp, defaultValue?: string | boolean): Command;
+    requiredOption<T>(flags: string, description: string, fn: (value: string, previous: T) => T, defaultValue?: T): Command;
 
 
     /**