Saves the editor into a file, returning #t if sucessful, #f otherwise.
The filename and format used to save the file can be retrieved with get-filename. In a text% instance, the format can be retrieved with get-file-format.
See also on-save-file, after-save-file, and can-save-file?.
If filename is #f, then the internally stored filename will be used; if filename is "" or if the internal name is unset or temporary, then the user will be prompted for a name. The possible values for format are described at load-file. If show-errors? is #f, then error messages reporting save errors (printed to stdout) are suppressed.