Added update "column = !column"

Useful for changing booleans in DB.
Update like this:

...
$db->update("table", array("col_boolean" => $db->not()));

Fixing getOne to not error on 0 results

Adding a simple isset to check if res[0] is actually set, if so return it if not return null so we don't have a floating result.

Added count variable which stores returned rows count

Some readme improvements

Allow to pass bind variables for func()

More real example of func