Python 3 preparation: unicode. This patch introduces roundup/anypy/strings.py, which has a comment explaining the string representations generally used and common functions to handle the required conversions. Places in the code that explicitly reference the "unicode" type / built-in function are generally changed to use the new functions (or, in a few places where those new functions don't seem to fit well, other approaches such as references to type(u'') or use of the codecs module). This patch does not generally attempt to address text conversions in any places not currently referencing the "unicode" type (although scripts/import_sf.py is made to use binary I/O in places as fixing the "unicode" reference didn't seem coherent otherwise).