Dali-rp2

* updated RP2 dependency to latest version, which fixes 2 bugs in HIFO. If you're using HIFO be sure to use RP2 1.10 or better.
* tweaked documentation

* add top-level multi-thread support: it's now possible to run data loader plugins in parallel, using the -t option (which selects the number of parallel threads)
* added Nexo CSV input plugin
* Coinbase REST input plugin: added support for Coinbase Earn Reversals (due to CC refunds, etc.)
* BlockFI CSV input plugin: added new transaction types
* revised and improved all documentation
* added FAQs

* added country plugin infrastructure (US is the default country plugin). Default fiat is no longer hardcoded to USD (it now comes from the country plugin)
* updated generators and rest of the code to use the native fiat from the country plugin (previously it was hard coded as USD)
* the dali script has been renamed to dali_us to support the new country plugin architecture
* added exchange hint to pair converter API
* added Ledger CSV data loader
* added credit card spend transactions to Coinbase plugin
* renamed cache folder from .cache to .dali_cache
* updated documentation to reflect latest changes
* small additions and fixes to documentation and code

* added new pair conversion plugin infrastructure
* added support for currency conversion to transaction resolver (useful to support non-USD fiats from foreign exchanges)
* fixed PR 44: added configurable historical data behavior and improved caching
* small improvements to code and documentation

* fixed PR 35: added exchange_withdrawal transaction type to Coinbase plugin
* various documentation improvements
* updated RP2 dependency to 1.0.0

* fixed issue 34: sometimes Coinbase returns bad fiat data for crypto conversions (fiat amount of sale < fiat amount of buy). DaLI used to raise an exception: now it issues a warning and sets the fiat fee to 0
* Coinbase plugin: _process_transfer() refactoring