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.

cmd/syncthing/memsize_windows.go

@@ -26,7 +26,7 @@ var (
 	globalMemoryStatusEx, _ = syscall.GetProcAddress(kernel32, "GlobalMemoryStatusEx")
 )
 
-func memorySize() (uint64, error) {
+func memorySize() (int64, error) {
 	var memoryStatusEx [64]byte
 	binary.LittleEndian.PutUint32(memoryStatusEx[:], 64)
 	p := uintptr(unsafe.Pointer(&memoryStatusEx[0]))
@@ -36,5 +36,5 @@ func memorySize() (uint64, error) {
 		return 0, callErr
 	}
 
-	return binary.LittleEndian.Uint64(memoryStatusEx[8:]), nil
+	return int64(binary.LittleEndian.Uint64(memoryStatusEx[8:])), nil
 }