Schema a now "parsed" into C++-validator-objects in a first
step and then validation takes place with these objects.
Errors are now handled via a user-provided error-handler
allowing the user to collect all errors at once or bail out
when a certain threshold is reached. Fixes#36 and #8.
One (sub-)schema can now be referenced with different URIs. Fixes#9
JSON schema draft 7 is now supported. Fixes#35
