Streams do not generally work well with RWops because
* streams have separate read and write pointers
* ostream doesn't allow you to determine how many bytes were actually written
* istream and ostream have separate set of functions
Try my best to support streams in RWops though, engaging some template
magic:
* provide separate template implementations of all operations which
depend on whether stream is an istream or ostream. This allows to
e.g. return 0 immediately for an attempt to write() to istream.
* disallow StreamRWops for classes which are both istream and ostream
to not run into ambiguity of separate read/write pointers
* for read failure, but partially read object back to the stream to not
lose data for following read (not sure that e.g. fread behaves so
though; I'll anyway expect user to Seek() after read or write failure)
* for write failure, there's no way to avoid leaking partial data to the
stream
In general, it is best to use this container as read-only.
Also add tests for StreamRWops
