Formatting
Clean up save()/output() methods
Replace repeated if statements with switch statement
Add ability to change PNG quality
Error checking
Don't override source image resource
- allows non-destructive chaining of operations
Allow scale() to work for > 100%
Significant rewrite of crop() and resize() methods
- move actual image manipulation to output()/save() so we can handle transparency better
- this allows changing between image types to work properly
- output header when rendering image directly in browser
- fix crop() method