Make fields of struct Signature public

- Update aarch64 feature related code
- Update benchmarks to last lib updates
- Apply Clippy fixes

Update rust to 2021 and deps

Update to last Poseidon version (which includes the changes of the reference implementation from
26ddaa91db)

Compatible with update at circomlib
(cf853c1cc9)

- Update EdDSA to last circomlib version
	- Compatible with circomlib version 0.3.0 at
	  5935ac69df
	- Use blake hash precandidate (non-blake2b) for circomlib
	  compatibility
	- Add circomlib testvector
- Change PrivateKey from BigInt to [u8;32], which lead to faster
signature computation:
	(Benchmarks on a Intel(R) Core(TM) i7-8705G CPU @ 3.10GHz, with
	32 GB of RAM)
	- Old:
	    ```
	    sign                    time:   [559.84 us 568.41 us 576.26 us]
	    verify                  time:   [376.59 us 376.68 us 376.78 us]
	    ```
	- New:
	    ```
	    sign                    time:   [383.85 us 390.31 us 396.44 us]
	    verify                  time:   [371.33 us 376.06 us 381.19 us]
	    ```
- crate version v0.0.5