Upgrade to v3.0.0

* integrate Medoo framework (medoo.in), old database handlers are
abandoned
(including sqlbuilder, dbresult), now only mysql and sqlite supported
TODO: add more database support (mainly to get tables and columns
information for different database types)
* Change configuration file to php way
* Add cmdQueue as a widget, old widget abandoned
* Make fpager module also support Windows (bins are stored in
drivers/fpager)
* Add ini module, which can read and write ini settings
* Move cache module to core
* Simplify 500 and 404 page
* Change the widget calling way.
Original: pw\widget('widgetname') -> pw\widget::widgetname(index,
config)
Support runtime config
* Support runtime db configuration
* Upgrade dataTables to 1.10.1, as well as the server side API
dataTablesAjax in pager module
* Change validator module to just pass name to it, values will be got
automatically, such as by $_GET