Fix broken links to papers

[Tomatosoup97]

• Contextual Effect Polymorphism was pointing to First-class Named Handlers
• Design and Implementation of Effect Handlers for Object-Oriented Programming Languages had broken link so I've changed that to dblp entry

[dhil]

Thanks. I will look into this PR after I have fixed the CI failure.

The CI fails because of a SSL error

 Error checking URL https://scm.iis.sinica.edu.tw/pub/2020-denot.pdf: HTTPSConnectionPool(host='scm.iis.sinica.edu.tw', port=443): Max retries exceeded with url: /pub/2020-denot.pdf (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1131)')))

Judging from #150 this seems to have been a problem for a while.