Added a percentReszie() method

Added `percentReszie()` method to quickly increase or decrease the image size to given percent. 

If want to increase the size use positive integer. If want to decrease the size use negative integer.

Example uses:

`Image::open()->percentReszie(50)->html('Re-sized to 50 percent')`

`Image::open()->percentReszie(-50)->html('Re-sized to negative 50 percent')`