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

(being respectful with occurences that might change the behaviour, i.e. default database prefixes)

Deprecate SimpleSAML_Default::initLogin() and move it to SimpleSAML_Auth_Source as a non-static method.

Move SimpleSAML_Auth_Default::handleUnsolicitedAuth() to sspmod_saml_Auth_Source_SP::handleUnsolicitedAuth() and deprecate the former.

Move SimpleSAML_Auth_Default::extractPersistentAuthState() to SimpleSAML_Auth_State::extractPersistentAuthState() and deprecate the former.