tag.Save: Prevent chmod, create instantly newFile with correct perms
tag.Save: Prevent chmod, create instantly newFile with correct perms

benchmark                              old ns/op     new ns/op     delta
BenchmarkParseAllFrames-4              195933        218706        +11.62%
BenchmarkParseAndWriteCommonCase-4     9601443       9942364       +3.55%
BenchmarkParseAndWriteManyFrames-4     11113784      10244006      -7.83%

benchmark                              old allocs     new allocs     delta
BenchmarkParseAllFrames-4              94             94             +0.00%
BenchmarkParseAndWriteCommonCase-4     78             76             -2.56%
BenchmarkParseAndWriteManyFrames-4     125            122            -2.40%

benchmark                              old bytes     new bytes     delta
BenchmarkParseAllFrames-4              527797        527753        -0.01%
BenchmarkParseAndWriteCommonCase-4     414290        414439        +0.04%
BenchmarkParseAndWriteManyFrames-4     419737        419440        -0.07%

bogem/id3v2