It was already added under 1.15

Change the extension of the documentation files from .txt to .md so that they can processed as markdown and displayed in github.

Fixes #379

Revert the new configuration option for the core:PHP authproc. Since we need to serialize authprocs and SP metadata in the state array, and closures are not serializable, it doesn't work. We could create a new module with this, adding a dependency on opis/closure 2.0.* or equivalent, to be able to serialize closures.

Added support for the full SCHAC 1.5.0 schema, including new attribute mappings between the old namespace in TERENA and the new urn:schac namespace.