Oda-data

Fixed

* The ODA GNI indicators, which returned mostly invalid data from the source
* A typo in the ODA GNI indicator name
* How `ODAData` deals with adding shares to indicators for which shares don't make sense

Changed

* Download data for indicator automatically if not available in data folder

Changed

* `ODAData().load_indicator()` now accepts a list of indicators as input.

Added

* A method to ODAData in order to add a "share" column to the output data.
* A method to ODAData in order to add a "gni_share"" column to the output data.

Added

* A total (ODA + OOF, excluding export credits) indicator for the CRS

Changed

* Changed how indicators are grouped when requesting a 'one' indicator.
instead of returning fewer columns than the raw indicators, it will return the
same columns, excluding the ones that make up the requested indicator

Added

* The ability to request a 'one_linked' indicator. These indicators are composed of a main indicator
which is _completed_ by a fallback indicator, when the values are missing. For example, In-Donor Refugee Costs
should be the same in Grant Equivalents or Flows. If the values are missing in the former, they are filled by the
latter.
* An option to get a simplified/summarised dataframe. Calling `.simplify_output_df()` on the `ODAData` object will
* keep only the requested columns, applying a `.groupby().sum()` on the remaining columns.
* Added documentation for the `ODAData` class

Added

* More comprehensive tests of all core functionalities
* A tool to extract CRS codes from the DAC CRS code list