Support fetching all currencies ledgers

[mnowotnik]

Description

Add support for fetching ledgers for all currencies.

Motivation and Context

Fetching ledgers for all currencies is supported by the REST API, but not by this lib:
https://docs.bitfinex.com/reference/rest-auth-ledgers

Type of change

• New feature (non-breaking change which adds functionality);

Checklist:

• I've done a self-review of my code;
• I've made corresponding changes to the documentation;
• I've made sure my changes generate no warnings;
• mypy returns no errors when run on the root package;

• I've run black to format my code;
• I've run isort to format my code's import statements;
• flake8 reports no errors when run on the entire code base;