@spec from_pem(
  String.t(),
  :public_key.pki_asn1_type() | [:public_key.pki_asn1_type()]
) :: [tuple()]

Scans the given string for PEM encoded entities.

An optional list of data types may be specified to filter the result down to entries of the given types. If an empty list is specified (the default), the result is not filtered.