- A warm up run is done and not timed to allow for any allocation of
  room for output data without accounting for it in the run times.
Previously this time spent allocating memory would be included in the
time we measured for the benchmark.

- Benchmarks are run multiple times and we then compute some statistics
  about the run time of the benchmark to give a better picture of the
expected run time of the function. To this end we run the benchmark
either 500 times or for 1.5s, whichever comes sooner (though these are
easily changeable). We then perform outlier limiting by Winsorising the
data (similar to how Rust's benchmarking library works) and print out
the median, mean, min and max run times along with the median absolute
deviation and standard deviation.

- Because benchmarks are run many times they can now perform some
  initial setup in the constructor, eg. to fill some test input data
array with values to let the main benchmark loop run faster.

- To allow for benchmarks to have members of the data type being
  benchmarked the struct must now be templated on this type, leading to
a bit of awkwardness. I've worked around this by adding the
`VTKM_MAKE_BENCHMARK` and `VTKM_RUN_BENCHMARK` macros, the make
benchmark macro generates a struct that has an `operator()` templated on
the value type which will construct and return the benchmark functor
templated on that type. The run macro will then use this generated
struct to run the benchmark functor on the type list passed. You can
also pass arguments to the benchmark functor's constructor through the
make macro however this makes things more awkward because the name of
the MakeBench struct must be different for each variation of constructor
arguments (for example see `BenchLowerBounds`).

- Added a short comment on how to add benchmarks in
  `vtkm/benchmarking/Benchmarker.h` as the new system is a bit different
from how the tests work.

- You can now pass an extra argument when running the benchmark suite to
  only benchmark specific functions, eg. `Benchmarks_TBB
BenchmarkDeviceAdapter ScanInclusive Sort` will only benchmark
ScanInclusive and Sort. Running without any extra arguments will run all
the benchmarks as before.