Decode unicode surrogate pairs

Prevents "System.ArgumentOutOfRangeException: A valid UTF32 value is between 0x000000 and 0x10ffff, inclusive, and should not include surrogate codepoint values (0x00d800 ~ 0x00dfff)."
Merge branch 'master' of git://github.com/CaptainCodeman/SGMLReader into CaptainCodeman_master
Removed warning causes by unused variable.