GitHub has specified FUNDING.yml, a file to include in a git repo for
pointing people to donation links.  Since F-Droid also points people
to donation links, this parses them to fill out Donate:
and OpenCollective:.  Specifying those in the metadata file takes
precedence over the FUNDING.yml.  This follows the same pattern as how
`fdroid update` includes Fastlane/Triple-T metadata.  This lets the
git repo maintain those specific donations links themselves.

https://help.github.com/en/articles/displaying-a-sponsor-button-in-your-repository#about-funding-files

The test file was generated using:

```python
import os, re, yaml

found = dict()
for root, dirs, files in os.walk('.'):
    for f in files:
        if f == 'FUNDING.yml':
            with open(os.path.join(root, f)) as fp:
                data = yaml.safe_load(fp)
            for k, v in data.items():
                if k not in found:
                    found[k] = set()
                if not v:
                    continue
                if isinstance(v, list):
                    for i in v:
                        found[k].add(i)
                else:
                    found[k].add(v)

            with open('gather-funding-names.yaml', 'w') as fp:
                output = dict()
                for k, v in found.items():
                    output[k] = sorted(v)
                yaml.dump(output, fp, default_flow_style=False)
```