Climate-finance

- Fixes a bug which prevented users from getting all providers by not specifying them (leaving `providers` as None).
- Fixes a bug where the data wouldn't necessarily be stored in the desired user-defined folder.
- Adds additional columns to the CRS used for analysis.

- Adds functionality to accept "providers" as OECD codes, ISO3 codes, or provider names.
- Adds functionality to get the list of available providers (`ClimateData.available_providers()`).
- Adds functionality to get groups of providers (like DAC, non-DAC, etc.). See the
documentation for more information.

- Fixes a bug where data was not being converted to other currencies when current prices
were selected.

- First release on PyPI.