2. reset current tile number to zero when EOC is detected in header

2. decode: store mode_switch instead of coding style in header

to errors from kdu that don't appear on osx or windows

allow passing nullptr to image format classes: this re-enables decode to stdout and encode from stdin

decode: added warning for user when compressed file contains XMP or IPTC data, and the format for decoded file does not support

storage of this data