while here:
- remove utf8/utf8_stream.h, now we only need utf8/utf8.h to include
- add some new methods for converting from a utf8 stream to wide stream/string
- do some improvements in TextStream:
- don't use temporary objects to convert utf8/wide
- add put_stream() which takes TextStreamBase<> as its argument
(uses an iterator instead of get_char() for reading)
- let operator<<(const Space & space) serialize to json and not to Space
there are methods for reading from string/files there
those methods were moved from SpaceParser and CSVParser
fixed: CSVParser didn't set input_as_utf8 flag