v1.1.18

This is a minor release that:

1. Improves the behaviour of ParsedNamespaces (allowing mutations and copying).
2. Allows for different default namespaces for read vs. write operation in databases.

Note: The default namespace changes only affects tables that are specified without a value for the appropriate schema field, and so should not break any existing implementations. Note that this was always intended to behave like this for (e.g.) dataframe_to_table operations, but this behaviour was masked by an earlier parsing of the namespaces.