Raise the "always encode as literal" size threshold from 4 to 14.
Raise the "always encode as literal" size threshold from 4 to 14.

This isn't an optimization per se, although it does trade off the
"encode 10 bytes" benchmark to favor speed over output size. The point
of this commit is to move closer to what the C++ snappy code does.

benchmark                     old MB/s     new MB/s     speedup
BenchmarkWordsEncode1e1-8     5.77         674.93       116.97x
BenchmarkWordsEncode1e2-8     47.96        47.92        1.00x
BenchmarkWordsEncode1e3-8     190.33       189.48       1.00x
BenchmarkWordsEncode1e4-8     190.25       193.17       1.02x
BenchmarkWordsEncode1e5-8     150.65       151.44       1.01x
BenchmarkWordsEncode1e6-8     180.11       180.63       1.00x
BenchmarkRandomEncode-8       4782.70      4700.25      0.98x
Benchmark_ZFlat0-8            372.49       372.12       1.00x
Benchmark_ZFlat1-8            186.49       187.62       1.01x
Benchmark_ZFlat2-8            4979.47      4891.26      0.98x
Benchmark_ZFlat3-8            85.76        86.16        1.00x
Benchmark_ZFlat4-8            566.31       570.31       1.01x
Benchmark_ZFlat5-8            366.01       366.84       1.00x
Benchmark_ZFlat6-8            162.13       164.18       1.01x
Benchmark_ZFlat7-8            153.69       155.23       1.01x
Benchmark_ZFlat8-8            167.91       169.62       1.01x
Benchmark_ZFlat9-8            147.71       149.43       1.01x
Benchmark_ZFlat10-8           414.06       412.63       1.00x
Benchmark_ZFlat11-8           248.87       247.98       1.00x

golang/snappy,FactomProject/snappy-go,FactomProject/snappy-go,golang/snappy