This patch ensures if `MCPlatformWaitForEvent` will return true if either
it found an event in the specified time or it ran a modal session which
will trigger event handling for the target window.

This patch adds the `without waiting` clause to the modal and sheet subwindow
commands.

                                                                                
This patch adds the `without waiting` clause to the go as modal and sheet   
commands.

                                                                                
This patch adds a parameter to `MCStack::openrect` to wait while opening. This
param replaces the previous implicit wait while opening behavior when the
window mode was modal or sheet.

This patch adds a release note for the new `without waiting` clause in the
`modal`, `sheet` and `go` commands.

This patch updates the `go`, `modal` and `sheet` commands to document the new
`without waiting` clause for modal and sheet dialog boxes.

This patch adds  test for the subwindow without waiting clause.