Support "readonly" as a parameter property.

[lddubeau]

Versions

typedoc: 0.5.1
typescript: 2.0.10

Steps to Reproduce

1. Create a project with this file named test.ts:

   class Foo {
       constructor(private a: string, readonly b: string) {
       }
   }
   
   const f: Foo = new Foo("1", "2");
   
   console.log(f.b);
   

2. Run typedoc on it.

Expected Results

The documentation should list both a and b as properties of the class Foo.

Actual Results

Only a is present as property of Foo but b is missing. (They both appear as parameters to the constructor, which is fine.)

[aciccarello]

Thanks @lddubeau. PRs are welcome.