Including <iostream> has two problems:
* Compile times are worse because of over-inclusion
* Binary sizes are worse when statically linking libstdc++ because
iostreams cannot be dead-code-stripped
simdjson only needs std::ostream. Include the header declaring only what
we need (<ostream>), omitting stuff we don't need (std::cout and its
initialization, for example).
This commit should not change behavior, but it might break users who
assume that including <simdjson/simdjson.h> will make std::cout
available (such as many of simdjson's own files).
John Keiser