3.28.0

Few interface changes, but some significant behavioural ones:

• Remove Certifi dependency and rely on root store
• Bump vendored hex_core to 0.20.1
• Improve description of rebar3 ct --dir option

Note that both the hex_core update and the certifi update are required for security. The removal of Certifi switches Rebar3 to use your operating system's root store, which may cause issues in some limited devices. However, since distrusted intermediary certificates are currently still in Certifi's hex package, we consider it safer to rely on operating system root stores.

If your device does not comply with the expected root store, you can configure one with {ssl_cacerts_path, "/path/to/cacerts.pem"}.