Changes:
- Allow user-defined databases to override bundled/system databases, see details below (35)
The loading order has been changed, which allows more customization. In the comparison below, note that later entries override earlier matching entries during loading.
Old loading order:
1. `paths` argument (default is empty)
2. bundled files, if `load_bundled=True` (default is true)
3. `xml` argument (default empty)
4. common folders, if `load_common=True` (default is true)
New loading order:
1. bundled files, if `load_bundled=True` (default is true)
2. common folders, if `load_common=True` (default is true)
3. `paths` argument (default is empty)
4. `xml` argument (default empty)