Include Modifiable at the top-level (#534)

* feat: include Modifiable at the top-level

* chore: update changelog

Author: gadomski

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - PySTAC Client specific warnings [#480](https://github.com/stac-utils/pystac-client/pull/480)
 - Support for fetching and merging a selection of queryables [#511](https://github.com/stac-utils/pystac-client/pull/511)
 - Better error messages for the CLI [#531](https://github.com/stac-utils/pystac-client/pull/531)
+- `Modifiable` to our public API [#534](https://github.com/stac-utils/pystac-client/pull/534)
 
 ### Changed
 

pystac_client/__init__.py

@@ -3,9 +3,11 @@
     "CollectionClient",
     "ConformanceClasses",
     "ItemSearch",
+    "Modifiable",
     "__version__",
 ]
 
+from pystac_client._utils import Modifiable
 from pystac_client.client import Client
 from pystac_client.collection_client import CollectionClient
 from pystac_client.conformance import ConformanceClasses