Add sharpen operation to png im4java resize

As requested form @paperboyo, this adds a sharpen operation to our png resizing.

### Before
![felicitycloake-normal](https://cloud.githubusercontent.com/assets/80089/4952783/da884a7e-6678-11e4-801a-f30de5e9a2cf.png) 

### After
![felicitycloake-sharpen](https://cloud.githubusercontent.com/assets/80089/4952786/df86ec92-6678-11e4-81cc-322ea08a1df0.png)

/cc @robertberry