mapping-commons/sssom-py: v0.3.20

• help CLI command by @hrshdhgd in https://github.com/mapping-commons/sssom-py/pull/335
• Labels not required while parsing obo-json by @hrshdhgd in https://github.com/mapping-commons/sssom-py/pull/331
• Clarifies possible doc format in --help docstrings by @hrshdhgd in https://github.com/mapping-commons/sssom-py/pull/336
• Fix issue where label is missing for an id in obographs parser by @matentzn in https://github.com/mapping-commons/sssom-py/pull/337
• Corrected flag and remove blank prefixes by @hrshdhgd in https://github.com/mapping-commons/sssom-py/pull/338

Full Changelog: https://github.com/mapping-commons/sssom-py/compare/v0.3.19...v0.3.20