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.

internal/lamport/clock.go

@@ -21,11 +21,11 @@ import "sync"
 var Default = Clock{}
 
 type Clock struct {
-	val uint64
+	val int64
 	mut sync.Mutex
 }
 
-func (c *Clock) Tick(v uint64) uint64 {
+func (c *Clock) Tick(v int64) int64 {
 	c.mut.Lock()
 	if v > c.val {
 		c.val = v + 1