Added max length parameter for GenericStringStream

[jonatanolofsson]

To protect the reader from reading too far in a non null-terminated buffer.

[jonatanolofsson]

I have not yet had the opportunity to verify this commit yet, but I'm putting it here as an implementation example for review and discussion.

[pah]

This is a duplicate of #789.

You might want to check out #158 or directly use the provided MemoryStream.

[jonatanolofsson]

Sorry I missed that, I did try to search =)

Thanks!