Revision 25

(Frodo) Parsing of both MBM and Sketch files finished and correct!

To do:
  * Need to ask ImageMagick what output formats are available;
  * Need to display those formats in --help, and understand them on the
    command-line;
  * Need to generate the correct type of file;
  * Need to take a look at some special Sketch options (size, cuts, etc)
  * Sometimes, the file seems to be negative. Probably an ImageMagick
    problem.
  * Need to handle several images in one file elegantly