Escape log lines

As discussed in #5
@kisielk Okay. I think this is really awesome!

Like you suggested, I changed the line to 

```go
buf := make([]byte, 0, 3*(len(host)+3+len(username)+2+26+3+len(req.Method)+1+len(uri)+1+len(req.Proto)+2+3+1+8)/2)
```

And these are the results:

```
$ go test -v -bench . -benchmem
=== RUN TestCompressHandler
--- PASS: TestCompressHandler (0.00 seconds)
=== RUN TestMethodHandler
--- PASS: TestMethodHandler (0.00 seconds)
=== RUN TestWriteLog
--- PASS: TestWriteLog (0.00 seconds)
=== RUN TestWriteCombinedLog
--- PASS: TestWriteCombinedLog (0.00 seconds)
PASS
BenchmarkWriteLog	 1000000	      1501 ns/op	     210 B/op	       5 allocs/op
```

Lesser B/op and allocs/op.

Should I include this change in the pull request?