format for enums

Other packages like github.com/xeipuuv/gojsonschema support writing

jsonschema="enum=val1,val2"

instead of

jsonschema="enum=val1,enum=val2"

Shouldn't invopop support this more concise format, too?

The issue names no files, tests, or entry points. Locate the code that parses jsonschema enum tags and its existing tests, then verify that the concise enum=val1,val2 form is accepted alongside the repeated form and produces the expected schema.

Written by the indexing model from the issue text.