consistent naming: encryption_algorithm should be encryptionAlgorithm

[recipe]

The encryption_algorithm option should be named as encryptionAlgorithm to be consistent.
7b4d4a6

Internally we keep onelogin/php-saml configuration with snake_case keys to be consistent with our own configuration naming conventions. Before creating the php-saml instance we transform all php-saml related keys to CamelCase and use this array to satisfy php-saml naming conventions. Now we will have to create a special rule for this single option to not to convert to CamelCase.

[pitbulk]

@recipe You are right, we should fix it by deprecating the use of encryption_algorithm (basically remove its use on demos and documentation) and in order to keep the backward compatibility read the possible values from encryption_algorithm and encryptionAlgorithm giving priority to the latest.

Can you contribute with a PR?