Use ImageMagick

[respectTheCode]

This is what I ended up doing and it is working well. If you have a better idea of how it should be configureable let me know.

Related to #23

[aheckmann]

released in 1.0.0 - there is now an imageMagick option.

you can either subclass gm with the option which returns a new constructor with the imageMagick option set:

var imageMagick = gm.subclass({ imageMagick: true })
// imageMagick is now a subclass of gm and will apply the imageMagick
// option for every operation

imageMagick(someImg).autoOrient().write(...)

or you can use imageMagick as a one-off:

gm(someImg).autoOrient().options({ imageMagick: true}).write(...)