Add SC proof generator (siblings)

Upgrade linter rules

Rm db.Info, rm go-iden3-core dependency, update version of
go-iden3-crypto

Fix loading root key

Add lvl on proof siblings for circom compatibility

Add extra level on circom siblings proof generation for circom circuits
compatibility.

Update Circom proofs for compatibility, add parsers

Update Circom proofs for compatibility,add parsers.

CircomProcessorProof & CircomVerifierProof have been tested to be
compatible into a circom circuit at versions:
```
"circom": "0.5.27",
"circomlib": "0.2.4"
```

Feature/update

Fix Hash bytes & *big.int parsers

Add pebble Batch implementation for db.Tx, and update db.Tx Put & Add methods
to return error.

Add CircomProofs for Addition & Update

Add mt.Update(key, value) method

Add mt.Get to retrieve a value for the given key

Add own db (storage) package with db.Storage interface, with Memory & Leveldb
implementations, and with tests.

Adapted with several changes from
https://github.com/iden3/go-iden3-core/tree/v0.0.8/db

Add mt.Delete(key) with test vectors

Correction to the GraphViz function when drawing empty nodes

Add GHA