Merge pull request #187 from PrivateStorageio/186.configurable-voucher-value

.circleci/config.yml

docs/source/configuration.rst

src/_zkapauthorizer/_plugin.py

src/_zkapauthorizer/configutil.py

src/_zkapauthorizer/resource.py

src/_zkapauthorizer/tests/strategies.py

src/_zkapauthorizer/tests/test_client_resource.py

src/_zkapauthorizer/tests/test_plugin.py