Writes out the contents of this CRichEditCtrl object to the specified output stream.
The value of nFormat must be one of the following:
SF_TEXT Indicates writing text only.
SF_RTF Indicates writing text and formatting.
SF_RTFNOOBJS Indicates writing text and formatting, replacing OLE items with spaces.
SF_TEXTIZED Indicates writing text and formatting, with textual representations of OLE items.
Any of these values can be combined with SFF_SELECTION. If SFF_SELECTION is specified, StreamOut writes out the current selection into the output stream. If it is not specified, StreamOut writes out the entire contents of this CRichEditCtrl object.
In the EDITSTREAM parameter es, you specify a callback function which fills a buffer with text. This callback function is called repeatedly, until the output stream is exhausted.