add doxygenation, improve object creation, improve sqlite db object, improve module

Code is partially documented.
When creating a user object, the destructor is automatically sourced, so
no Delete function is needed.
DB object now uses Statement objects, instead of managing statements
manually (there was also a leak, since those statements weren't being
finalized.  Yaaay RAII).
Module now uses its registry for main, init, and cleanup, instead of
managing them on the stack entirely.