See #73

All minor. Including an update from rust-bitcoin v0.31.1 to v0.31.2.

By default runs the bitcoin version

```shell
$ nix run .
Config { log: StdErrLog { verbosity: Error, quiet: false, show_level: true, timestamp: Off, modules: [], writer: "stderr", color_choice: Auto, show_module_names: false }, network_type: Bitcoin, db_path: "./db/mainnet", daemon_dir: "/home/casatta/.bitcoin", blocks_dir: "/home/casatta/.bitcoin/blocks", daemon_rpc_addr: 127.0.0.1:8332, cookie: None, electrum_rpc_addr: 127.0.0.1:50001, http_addr: 127.0.0.1:3000, http_socket_file: None, monitoring_addr: 127.0.0.1:4224, jsonrpc_import: false, light_mode: false, address_search: false, index_unspendables: false, cors: None, precache_scripts: None, utxos_limit: 500, electrum_txs_limit: 500, electrum_banner: "Welcome to electrs-esplora 0.4.1", electrum_rpc_logging: None }
```

But it contains also a package with the liquid variant:

```shell
$ nix run .#blockstream-electrs-liquid -- --network liquid
Config { log: StdErrLog { verbosity: Error, quiet: false, show_level: true, timestamp: Off, modules: [], writer: "stderr", color_choice: Auto, show_module_names: false }, network_type: Liquid, db_path: "./db/liquid", daemon_dir: "/home/casatta/.bitcoin/liquidv1", blocks_dir: "/home/casatta/.bitcoin/liquidv1/blocks", daemon_rpc_addr: 127.0.0.1:7041, cookie: None, electrum_rpc_addr: 127.0.0.1:51000, http_addr: 127.0.0.1:3000, http_socket_file: None, monitoring_addr: 127.0.0.1:34224, jsonrpc_import: false, light_mode: false, address_search: false, index_unspendables: false, cors: None, precache_scripts: None, utxos_limit: 500, electrum_txs_limit: 500, electrum_banner: "Welcome to electrs-esplora 0.4.1", electrum_rpc_logging: None, parent_network: Bitcoin, asset_db_path: None }
```

with this fix, on nixos you can build the project by doing:

```shell
$ nix develop # ensure dependencies to build
$ cargo build # succesfully build
```

otherwise there is an error in building rocksdb