Add `-f` option to read input from an input file as context

[tk755]

Using $ q -f FILE [command] ... should read the contents of FILE and pass it as context to the command.

This will enable more useful file parsing like so:

$ q -f README.md -s install this program

This will also enable us to add a feature to image generation -- namely editing input images (currently we can only generate images):

$ q -f input_image.png -i convert this image to the style of the Simpsons