wxFileCtrlBase: document constants
main: let set_style_flag_option return true if flag is used.
wxFilePicker: document constants and add protection for excluding style
flags ( open vs. save)
DirPicker: document constants, add protection for style flags.
change WX::Point to use wxRealPoint instead of wxPoint, but add
automatically converter
wxDC: add more properties and document them
AuiBook: document some constants and fix BookCtrl#get_page_image for
AuiBook