Cython optimizations; PyPI availability

• Major performance improvements with Cython
• More and better tests
• Available on PyPI
• No husl package dependency; just numpy is required

1.3.0

Optimizations! Runs 50 to 30% faster than 1.2.0 (if numexpr is installed) while consuming far less memory.

• using numexpr where it makes sense to reduce the memory overhead of lots of chained element-wise numpy operations
• laid the groundwork for choosing optimizations based on which libraries are available; if Cython is available and a function is decorated appropriately, the user will get the Cython version of that function, and so on.
• made a test fixture that exercises all available versions (standard numpy, numexpr-optimized, and cython-optimized) of the library for a given unit test

v1.2.0

Added basic handling of RGBA-shaped data that might come from .png files or from any color space that has an alpha channel.

v1.1.0

Added support for RGB -> HUSL conversions with grayscale images. This way users don't have to be concerned with the shape of their data. The nphusl functions will reshape and squeeze the data as needed to produce meaningful HUSL values.

v1.0.0

Conversion from RGB to HUSL and from HUSL to RGB fully tested and supported. No API changes planned for the foreseeable future, so this first release gets a major version number.