Fix conversion if (int x = foo()). Initial stream api. Extended enumset.

test/unit/stdlib/io/bytestream.c3

@@ -0,0 +1,25 @@
+module std::io @test;
+
+fn void! bytestream()
+{
+	ByteReader r;
+	r.init("abc");
+	Stream s = r.as_stream();
+	assert(s.len()? == 3);
+	char[5] buffer;
+	assert('a' == s.read_byte()?);
+	s.pushback_byte()?;
+	usz len = s.read(&buffer)?;
+	assert(buffer[:len] == "abc");
+	ByteWriter w;
+	w.init();
+	Stream ws = w.as_stream();
+	ws.write("helloworld")?;
+	assert(w.as_str() == "helloworld");
+	s.seek(0, SET)?;
+	ws.read_from(&s)?;
+	s.seek(1, SET)?;
+	s.write_to(&ws)?;
+	assert(w.as_str() == "helloworldabcbc");
+}
+