Implement beast::istream()

[djarek]

This would make the API symmetric in use. E.g.:

int i, j;
beast::istream(body) >> i;
beast::istream(body) >> j;

[vinniefalco]

This should be done by modifying detail::ostream_buffer to fulfill the get contract of std::basic_streambuf.

[stale[bot]]

This issue has been open for a while with no activity, has it been resolved?

[ivan-volnov]

I'm looking forward to have this feature implemented