remove unnecessary comments and commented out debug messages
use binary ppm encoding instead of ascii.

Cuts the file size in half.
Also allows for larger color range without increasing the file size
remove unnecessary hash_table cleanup.

hash_table_delete already does this.
Merge branch 'rampantmonkey-ppm_encoding'

Switch from PPM ASCII to PPM Binary file format. This uses triplets of chars to
represent the color of each pixel instead of triplets of integers. Consequently
the file size is cut in half.