Farbfeld

Changes

* Added [type hints](https://www.python.org/dev/peps/pep-0484/).
* Simplified component validation.

Changes

* Removed unnecessary `__all__` from the module.
* Fixed typos in docstrings.
* Added documentation for writing images.

Changes

* Simplified API:
* `read` now accepts a file object instead of `bytes`.
* Added functionality for writing farbfeld files:
* New `write` function for writing pixel data to file objects.
* Removed normalization code – this can be done trivially by libraries like NumPy.

This is the first public release.