o extend MemoryReadStream with XOR facility
o implement MemoryWriteStream
o _fileHandle now is a reference to BaseScummFile class and is created on the fly
o implement ScummNESFile class which is basically extract_mm_nes utility
o update NES MM md5's due to above changes
NOTE: to run MM NES now you need to remove *.LFL files and (probably) rename
ROM to standard conventional name 'Maniac Mansion (XXX).nes'
svn-id: r17300
