MongoDB::Connection is deprecated.

Made some Dancer::Session::MongoDB changes.
MongoDB::MongoClient has a new authenticate method for mongodb authentication.

for more infos: https://metacpan.org/pod/MongoDB::MongoClient#authenticate-dbname-username-password-is_digest

new directive in config.yml:
mongodb_is_digest: (true/false) for specifying given mongodb_password as a hash or cleartext.