Upgrade notes for SimpleSAMLphp 1.13

* The RSA_1.5 (RSA with PKCS#1 v1.5 padding) algorithm is now longer allowed by default. This means messages received
that use this algorithm will fail to decrypt.
* Several functions, classes and interfaces are now deprecated. Please check your code if you are using the API.
* A workaround related to performance issues when processing large metadata sets was included in **1.13.2**. **This workaround is experimental and could have unexpected side effects**.