Flatten concatenates multiple sets of buckets into a single slice.

NewExponential creates n exponential buckets, starting with the supplied initial value and increasing by a user-defined factor each time.

NewLinear creates n linear buckets, starting with the supplied initial value and increasing by a user-defined width.

NewRPCLatency returns a hand-crafted set of buckets useful for tracking the latency of RPCs (in milliseconds).