Update ArgsRenderer.hx. First optional argument wasn't rendered as optional in TS.

[mrEuler]

Here is an example of how it worked before:

Haxe:

class Vec3 {
    public inline function new(x:Float = 0, y:Float = 0, z:Float = 0) {
         ...
    }
}

TypeScript Declarations:

export class Vec3 {
    constructor(x: number, y?: number, z?: number);
}

After this fix ts declarations will look like:
TypeScript Declarations:

export class Vec3 {
    constructor(x?: number, y?: number, z?: number);
}

[elsassph]

Silly mistake...

[mrEuler]

I would also add some tests for functions because there were no tests for such situation