Fix : Router null response defined a bad HTTP code
Remove PSDF library

Markdown format is now the favorite content format
Herlper  load_library() now generates an error

c.f: new error guidelines
Response::headers() set parameter type
Mail library v2.7

Extended exception replaced by SPL ones
Settings constants becomes part of System package
cURL class v3.0.0
Core\View is now a part of Core package
Init constants becomes a part of System package