The flag name and its values match libpq's sslmode connection parameter. The default value (prefer) will first try an SSL connection; if that fails, it will try a non-SSL connection. Libpq documentation: https://www.postgresql.org/docs/14/libpq-connect.html#LIBPQ-CONNECT-SSLMODE
Move regression tests into a separate subdirectory. Update README in tests and covert it from org-mode to markdown. Also add 'make distcheck' to Travis CI testing.
