Implemented delete_entry command.
Changed returned values and parameters of database to use std::string instead of char*.
Removed cstdint usage.
Changed commands word separator from underscore to dash.
Implemented utility to parse int and verified if the given id on delete-entry is an valid integer.
Added utility function to empty file.
Added utility function to read file.
Implemented new-entry command.
Fixed method declaration/implementation order.
Changed flag name from shown to hidden.
Implemented hide/unhide entry command.