Feature to enable Neptune GPU Poseidon (#141)

* enable neptune gpu hashing

* Disable clippy on GPU

.github/workflows/rust.yml

@@ -30,5 +30,5 @@ jobs:
     - name: Check Rustfmt Code Style
       run: cargo fmt --all -- --check
     - name: Check clippy warnings
-      run: cargo clippy --all-targets --all-features -- -D warnings
+      run: cargo clippy --all-targets -- -D warnings
 

Cargo.toml

@@ -51,3 +51,5 @@ harness = false
 
 [features]
 default = []
+cuda = ["neptune/cuda", "neptune/pasta", "neptune/arity24"]
+opencl = ["neptune/opencl", "neptune/pasta", "neptune/arity24"]