Release v0.5.1

[gadomski]

Description:
Feature-adding, backwards compatible release. Useful to get the bugfix from #312.

PR Checklist:

• Code is formatted
• Tests pass
• Changes are added to the CHANGELOG

Annotated tag contents

v0.5.1

Added:

- Added `ItemSearch.url_with_parameters` to get a formatted search url [#304](https://github.com/stac-utils/pystac-client/issues/304)

Fixed:

- Fix variable name in quickstart example [#316](https://github.com/stac-utils/pystac-client/pull/316)
- `StacApiIO.write_text_to_href` [#312](https://github.com/stac-utils/pystac-client/pull/312)
- Removed mention of STAC_URL in `Client.open` docstring [#317](https://github.com/stac-utils/pystac-client/pull/317)