open_memory_file(+Handle, 
+Mode, -Stream, +Options)Open a memory-file as open_memory_file/3. 
Options:
- encoding(+Encoding)
- Set the encoding for a memory file and the created stream. Encoding 
names are the same as used with open/4. 
By default, memoryfiles represent UTF-8 streams, making them capable of 
storing arbitrary Unicode text. In practice the only alternative is octet, 
turning the memoryfile into binary mode. Please study SWI-Prolog Unicode 
and encoding issues before using this option.
- free_on_close(+Bool)
- If true(defaultfalse) and the memory file is 
opened for reading, discard the file (see free_memory_file/1) 
if the input is closed. This is used to realise open_chars_stream/2 
in library(charsio).