[Teton/Voyageurs] Subscribe to scancodes in teton and print them to screen.

Right now there appears to be an error with the font so that the
proper character is received but we write an incorect character to the
screen (off by one?).

lib/mammoth/ipc/port_server.cpp

@@ -47,4 +47,12 @@ glcr::ErrorCode PortServer::PollForIntCap(uint64_t *msg, uint64_t *cap) {
   return glcr::OK;
 }
 
+glcr::ErrorOr<char> PortServer::RecvChar() {
+  uint64_t bytes = 1;
+  uint64_t caps = 0;
+  char byte;
+  RET_ERR(ZPortRecv(port_cap_, &bytes, &byte, &caps, nullptr));
+  return byte;
+}
+
 }  // namespace mmth