Benchmark across Parse options, add memory benchmarking.

[suyashkumar]

This change updates the Parse benchmark to operate across useful ParseOptions, adds memory benchmarking, and updates some benchmark params.

For example, we can take a look at the CPU / memory differences across the new ParseOptions for one of the test dicoms:

BenchmarkParse/NoOptions/4.dcm-4                                              10     106876945 ns/op    120572543 B/op      2160 allocs/op
BenchmarkParse/SkipPixelData/4.dcm-4                                          10        531193 ns/op       34900 B/op       2144 allocs/op
BenchmarkParse/SkipProcessingPixelDataValue/4.dcm-4                           10       1807256 ns/op     7573518 B/op       2146 allocs/op