Unable to create large images

[dyyln]

Due to the way the pnghdr is constructed, the top 2 bytes of the width and height are missed.
This means you cannot create images with dimensions larger than 65,536.

Changing from this

				0,0,(uint8_t)(w >> 8),(uint8_t)(w), // width
				0,0,(uint8_t)(h >> 8),(uint8_t)(h), // height

to this :

				(uint8_t)(w >> 24),(uint8_t)(w >> 16),(uint8_t)(w >> 8),(uint8_t)(w), // width
				(uint8_t)(h >> 24),(uint8_t)(h >> 16),(uint8_t)(h >> 8),(uint8_t)(h), // height

Solves the issue in the header, but leaves the png corrupted, due to the data chunk being malformed in some way.