* add digitalocean_regions and digitalocean_region data sources
* add documentation for digitalocean_region[s] data sources
* fix required features filter to ensure each feature is present
* remove addition to go.mod
* fix links in sidebar
* switch datasource_digitalocean_regions to have `filter` and `sort` attributes
* introduce and use setResourceDataFromMap to simplify code sharing
Now flattened resources can be set easily on schema.ResourceData instances.
* refactor getDigitalOceanRegions and flattenRegion into separate file
* refactor getDigitalOceanRegions to return a slice instead of a map
* add test for missing slug for digitalocean_region data source
* update digitalocean_regions data source docs for the filter/sort change
* correct description in markdown header
* make digitalocean_regions be a list not a set
* use validation to ensure `slug` attribute is provided
Tom Dyas