First working release

Updates:
No user preprocessing required, aspect ratio of output fixed, API began.
Features:
API is not very useful; selects a random character if "darkness value" is already calculated.
Demo program (main.py) generates ASCII art straight from an image, allows selection of size and character set.
Upcoming:
Useful API (can take an image and output a 2-D list)
GIF support (3-D list)
JSON output? (In addition to list/.txt file output)