buffer history now: can't go out of bounds, can go to an empty line once you go past the most recent

module/buffer.lua

@@ -294,9 +294,14 @@ function buffer:read(...)
       elseif char == "B" then -- down
        hIndex = hIndex - 1
        io.write("\27[u"..(" "):rep(buffer:len()+1))
+       if hIndex == 0 then
+        hIndex = hIndex - 1
+        buffer = ""
+       end
        buffer = self.history[1+#self.history-hIndex] or buffer
        pos = 1
       end
+      hIndex = math.max(math.min(hIndex,#self.history),0)
      end
     elseif char == "\8" then
      if #buffer > 0 and pos <= #buffer then