Support 'blob_value' / 'blob_key_value' in datastore protobufs #233
Description
In addition to the scalar types we already support, there are the following value types we don't yet
support:
- 'entity_value' (PR Support entity protobufs #232)
- 'list_value' (issue Support list values in entities #223)
- 'blob_value' (see https://github.com/GoogleCloudPlatform/google-cloud-datastore/blob/6073e01540264db58ee50c30a1e9f006677eb794/proto/datastore_v1.proto#L115)
- 'blob_key_value' (see https://github.com/GoogleCloudPlatform/google-cloud-datastore/blob/6073e01540264db58ee50c30a1e9f006677eb794/proto/datastore_v1.proto#L111)