Improve rendering time

50% speedup.  Fix #91

to run the benchmark:

		go test -test.run=NONE -bench=".*" -test.benchmem=true ./transform/ > new.txt

to compare the results:

		/usr/local/go/misc/benchcmp baseline.txt new.txt

Speedup and memory improvements

		benchmark             old ns/op    new ns/op    delta
		BenchmarkChain           101219        50453  -50.15%
		BenchmarkTransform        51625        45531  -11.80%

		benchmark            old allocs   new allocs    delta
		BenchmarkChain              222          103  -53.60%
		BenchmarkTransform          135          106  -21.48%

		benchmark             old bytes    new bytes    delta
		BenchmarkChain            23919        10998  -54.02%
		BenchmarkTransform        11858        10665  -10.06%

transform/post.go

@@ -1,9 +1 @@
 package transform
-
-import (
-	"io"
-)
-
-type Transformer interface {
-	Apply(io.Writer, io.Reader) error
-}