Fast Hilbert

Fast Hilbert 2D curve computation using an efficient Lookup Table (LUT) and fast "orientation-stable encoding". The curve is slightly different compared to the original hilbert curve. Every odd iteration is oriented by 90 degrees:

• Orientation-stable encoding (all credits to DoubleHyphen see this PR for more information)
• Convert from discrete 2D space to 1D hilbert space and reverse
• No order or iteration input required
• Very fast using an efficient 512 Byte LUT
• Only one additional dependency.

Benchmarking the conversion from full 256x256 discrete 2D space to the 1D hilbert space, shows that fast_hilbert is about 12 times faster compared to the fastest 2D hilbert transformation libs written in rust. Benchmarked on a Intel i5-6400 CPU @ 2.70 GHz, 4 Cores with 8 GB RAM:

| Library | Time | Description | ----------------- |-----------:| ----------------- | | fasthilbert | 0.2 ms | Optimized for fast computation in 2D discrete space using an efficient *LUT* | hilbert2d | 2.5 ms | Also allows other variants such as Moore and LIU | | hilbert_curve | 2.0 ms | Implements algorithm described on Wikipedia | | hilbert | 32.1 ms | Allows computation of higher dimensional Hilbert curves |