Integer type policy

Integers are for numbers, enabling arithmetic like subtractions and for
loops without getting shot in the foot. Unsigneds are for bitfields.

- "int" for numbers that will always be laughably smaller than four
  billion, and where we don't care about the serialization format.

- "int32" for numbers that will always be laughably smaller than four
  billion, and will be serialized to four bytes.

- "int64" for numbers that may approach four billion or will be
  serialized to eight bytes.

- "uint32" and "uint64" for bitfields, depending on required number of
  bits and serialization format. Likewise "uint8" and "uint16", although
  rare in this project since they don't exist in XDR.

- "int8", "int16" and plain "uint" are almost never useful.

protocol.go

@@ -222,8 +222,8 @@ func (c *rawConnection) Request(folder string, name string, offset int64, size i
 	ok := c.send(id, messageTypeRequest, RequestMessage{
 		Folder: folder,
 		Name:   name,
-		Offset: uint64(offset),
-		Size:   uint32(size),
+		Offset: offset,
+		Size:   int32(size),
 	})
 	if !ok {
 		return nil, ErrClosed
@@ -706,8 +706,8 @@ func (c *rawConnection) pingerLoop() {
 
 type Statistics struct {
 	At            time.Time
-	InBytesTotal  uint64
-	OutBytesTotal uint64
+	InBytesTotal  int64
+	OutBytesTotal int64
 }
 
 func (c *rawConnection) Statistics() Statistics {