Make XML entity handling optional

[kousiktn]

I am using XML as an intermediate format for dumping words extracted from a PDF document and then reading them back.

When the PDF document itself containers strings like: "©", TinyXml treats them as one symbol rather than encoding them as "©". My content will never have a case where "©" will actually represent a copyright symbol and so this entity handling can be made optional(can be set to true by default).