Fixed : Function thumbnail (Adaptive resize) problem #35

imagecopyresampled can only take integers, so anything with decimal
places had the chance of resizing incorrectly.

This fixes the problem and all other examples. I’ve tested it lightly
and everything seems to work fine. I thought I would give the heads up
that it may need more testing.

I also added the aspect_ratio variables to the fit methods as I didn’t
see any reason to calculate it twice