adds func to draw crop frame and thirds grid
adds helper func to write png
use debug option
use current dir for debug images
adds images from smartcrop.js
fixes not using a gopher as example image
use a real gopher
adds license headers and package description
fixes crop dimensions
cleanup, small fixes
adds downsampling again, disabled atm
unexport helper functions
fixes test
Merge pull request #3 from michiwend/master

adds debugging output, fixes crop dimensions + other small changes