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