parse audience based on presence in description

[mikesndrs]

Summary of changes
Add target_audience based on presence of specific words in event description.

Motivation and context
Taxila scrapers

Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree
  to license it to the TeSS codebase under the
  BSD license.