slsdm 0.2.0

# Scikit-Learn SIMD DistanceMetrics (SLSDM)

## Install from pip
Run `pip install slsdm`. Note that the premade wheels are only built with support for `SSE2, SSE3` instructions.

## Install From Source:

1. Create a new environment with `xsimd`: `conda create -n <env_name> -c conda-forge python~=3.10.0 compilers`
2. Activate the environment: `conda activate <env_name>`
3. Run `pip install -e .`

**Warning**: At this point, building from source only works with `gcc`. Support for `clang` and `MSVC` is in progress.

## Specify SIMD Target Architectures

By default, `slsdm` will be built with `{SSE3, SSE2}` support. The preferred architectures can be specified at build time using the `SLSDM_SIMD_ARCH` environment variable by passing a comma-separated list of architecture specification tokens. Currently, only `x86_64` CPU features are supported. Specifically, the following features are available:
```
Instruction Set | Specification Tokens
======================================
AVX512BW        |     avx512bw
AVX512DQ        |     avx512dq
AVX512CD        |     avx512cd
AVX512F         |     avx512f
FMA4            |     fma4
FMA3 + AVX2     |     fma3, avx2
AVX2            |     avx2
FMA3 + AVX      |     fma3, avx
AVX             |     avx
FMA3 + SSE4.2   |     fma3, sse4_2
SSE4.2          |     sse4_2
SSE4.1          |     sse4_1
SSSE3           |     ssse3
SSE3            |     sse3
SSE2            |     sse2
```

For example, to build for `{SSE3, AVX, FMA 3 + AVX, AVX2}` one would specify `SLSDM_SIMD_ARCH="sse3, avx, fma3<xs::avx>, avx2"`.

You may also prefer to specify features *up to*, and optionally including, a certain instruction. For that, you may prepend a specification token with `<` (exclusive) or `<=` (inclusive). For example, to build for `{SSE2, SSE3, SSSE3, AVX2}` one would specify `SLSDM_SIMD_ARCH="<=ssse3, avx2"`.

You can also disable specific features that would otherwise be enabled by your specification by prepending the `~` symbol to the specification token. For example, to build for `{SSE4_2, SSE4_1, SSE3, SSE2}`, one would specify `SLSDM_SIMD_ARCH="<=sse4_2, !ssse3"`. Note that the specification will be resolved in a left-to-right order, so `SLSDM_SIMD_ARCH="!ssse3, <=sse4_2"` would not produce equivalent results, and indeed still generates `SSSE3` instructions.

To include `FMA3` combination instruction sets, include `fma3` in the `SLSDM_SIMD_ARCH` specification and any compatible instruction sets will automatically be enabled. For example, `SLSDM_SIMD_ARCH="fma3, <=avx"` will enable `{FMA3 + AVX, AVX, FMA3 + SSE4.2, SSE4.2, SSE4.1, SSSE3, SSE3, SSE2}`.

**Warning**: Runtime dispatch is not yet correctly supported. When distributing to other machines, please build only with SIMD sets that all target machines support.