Backend refactor (#120)

* remove spqlios, split cpu_ref and cpu_avx into different crates

* remove spqlios submodule

* update crate naming & add avx tests

poulpy-cpu-avx/README.md

@@ -0,0 +1,18 @@
+# 🐙 Poulpy-Backend
+
+**Poulpy-Backend-CPU-AVX** is a Rust crate that provides concrete implementations of **`poulpy-hal`**. This crate is used to instantiate projects implemented with **`poulpy-hal`**, **`poulpy-core`** and/or **`poulpy-schemes`**.
+
+## Example
+
+```rust
+use poulpy_backend_cpu_avx::FFT64Avx;
+use poulpy_hal::{api::ModuleNew, layouts::Module};
+
+let log_n: usize = 10;
+let module = Module<FFT64Avx> = Module<FFT64Avx>::new(1<<log_n);
+```
+
+## Contributors
+
+To add a backend, implement the open extension traits from **`poulpy-hal/oep`** for a struct that implements the `Backend` trait.  
+This will automatically make your backend compatible with the API of **`poulpy-hal`**, **`poulpy-core`** and **`poulpy-schemes`**.