Replace binary.Write with non-reflective code
Replace binary.Write with non-reflective code

This gives a multiplicative improvement on performance.

Comparing sequential writer and now:

benchmark                   old ns/op    new ns/op    delta
BenchmarkWrite                   9379         6184  -34.07%
BenchmarkWrite-2                 9712         3307  -65.95%
BenchmarkWrite-4                 9582         2078  -78.31%
BenchmarkWrite-8                 9569         2505  -73.82%
BenchmarkRoundtripFile    79623561221  70976393409  -10.86%
BenchmarkRoundtripFile-2  80254192655  37301227916  -53.52%
BenchmarkRoundtripFile-4  81799804517  25684943890  -68.60%
BenchmarkRoundtripFile-8  81108318809  28525533743  -64.83%

biogo.boom benchmarks for reference:

BenchmarkWriteBoom	 1000000	      2079 ns/op
BenchmarkWriteBoom-2	 1000000	      1842 ns/op
BenchmarkWriteBoom-4	 1000000	      1849 ns/op
BenchmarkWriteBoom-8	 1000000	      1826 ns/op
BenchmarkRoundtripFileBoom	       1	28708932700 ns/op
BenchmarkRoundtripFileBoom-2	       1	27754176754 ns/op
BenchmarkRoundtripFileBoom-4	       1	27720111150 ns/op
BenchmarkRoundtripFileBoom-8	       1	27411465395 ns/op

brentp/hts,biogo/hts