Improve performance when writes exceed max-values-per-tag or max-series

[stuartcarnie]

benchmark                                                                  old ns/op     new ns/op     delta
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxValuesExceeded-8        6175374       2714158       -56.05%
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxValuesNotExceeded-8     344502        326312        -5.28%
BenchmarkShardIndex_CreateSeriesListIfNotExists_NoMaxValues-8              346734        329961        -4.84%
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxSeriesExceeded-8        2414945       1996223       -17.34%

benchmark                                                                  old allocs     new allocs     delta
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxValuesExceeded-8        45377          128            -99.72%
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxValuesNotExceeded-8     33             20             -39.39%
BenchmarkShardIndex_CreateSeriesListIfNotExists_NoMaxValues-8              33             20             -39.39%
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxSeriesExceeded-8        15219          71             -99.53%

benchmark                                                                  old bytes     new bytes     delta
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxValuesExceeded-8        1354539       480114        -64.56%
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxValuesNotExceeded-8     2101          1261          -39.98%
BenchmarkShardIndex_CreateSeriesListIfNotExists_NoMaxValues-8              2100          1261          -39.95%
BenchmarkShardIndex_CreateSeriesListIfNotExists_MaxSeriesExceeded-8        707247        477737        -32.45%

---

Additional improvements to bytesutil packages

benchmark                           old ns/op     new ns/op     delta
BenchmarkContains_True-8            67.0          41.8          -37.61%
BenchmarkContains_False-8           73.2          47.6          -34.97%
BenchmarkSearchBytes_Exists-8       51.5          34.3          -33.40%
BenchmarkSearchBytes_NotExits-8     57.7          39.8          -31.02%

Required for all non-trivial PRs

• Rebased/mergable
• Tests pass
• CHANGELOG.md updated

[stuartcarnie]

@jwilder I will hold off merging this to master until TSI changes are merged. Once you review, I will cherry pick to 1.3 for a 1.3.9 release for Cisco