Add socket operations

examples/echoclient.monkey

@@ -0,0 +1,8 @@
+#!./monkey-lang
+
+fd := socket("tcp4")
+bind(fd, "127.0.0.1:32535")
+connect(fd, "127.0.0.1:8000")
+write(fd, "Hello World")
+print(read(fd))
+close(fd)

examples/echoserver.monkey

@@ -0,0 +1,11 @@
+#!./monkey-lang
+
+fd := socket("tcp4")
+bind(fd, "0.0.0.0:8000")
+listen(fd, 1)
+
+nfd := accept(fd)
+msg := read(nfd)
+write(nfd, msg)
+close(nfd)
+close(fd)