Add max level support

[nickbroon]

This modified version contains support for a maximum include level to output, by perform a breadth first sort. https://github.com/dagget/programming/tree/master/perl/cinclude2dot-ng
It would be good to merge this option.

[code-hunger]

Url seems to have changed: https://github.com/dagget/programming/blob/master/perl-scripts/cinclude2dot-ng/cinclude2dot-ng