Add flags enumeration support to prototypes

[kennux]

They should be specified in XML like a collection and parsed into the enum field.
Example:

<fieldName>
  <li>enum1</li>
  <li>enum3</li>
</fieldName>

public class TestObj : IPrototype
{
public TestEnum fieldName; // Should be TestEnum.test with xml above
}
[System.Flags]
public enum TestEnum {
enum1 = 1,
enum2 = 2,
enum3 = 4,
test = enum1 | enum3
}