Core: Added DNET_DEFAULT_WAIT_TIMEOUT_SEC to core.h
Core: Added public dnet_digest_*transform methods

This methods are public interfaces for internal sha512 implementation.
dnet_digest_auth_transform is public hmac-sha512 implementation.
License: Change license from GPL to LGPL
License: Added license information to files
Merge pull request #263 from euroelessar/master

Added hmac-sha512 impl & license fixes