Add dye API, canvas loading, future tests

The provisional API generates structured dye data from a dye string, and
dyes an image when provided dyeable image data and the associated dyeing
data.

The splitting of an image URI and the dye string should probably be
handled by a resource manager.

Tests are distinguished between stable tests and future tests.
Stable tests should pass at all times. Future tests should pass once
implemented, and be moved to stable test suites.
To run the future tests as well, run ./todo.sh.

The current logic to load and extract image data should probably be
refactored out from the test file and into some common file or resource
manager file.

Might need a custom assertion function for comparing image data to avoid
flooding the console if something doesn't fully match.

Finally, declare "use strict".