[Freetype] Doc typo: FT_Open_Args

[Burton Radons]

In the FreeType 2 documentation on FT_Open_Args, it refers to
"stream_type" in the Notes, which I can't make head nor tails of; I
assume it's supposed to be describing the flags field, but the value
names and usage context are all wrong, and it doesn't describe a few
enumerations.  Clarification and reassurance that unused fields don't
need to be set to a value (Unless, of course, if they do) would be
helpful.