Display bytes in base-ten format

[PointKernel]

Similar to #47

This PR updates the code thus numbers of bytes are displayed in base-ten format. i.e. B, MB, KB and GB.

[jrhemstad]

Seems like we should enable people to choose.

Maybe something like this:

enum class base { TWO, TEN };
template <typename ElementType>
void add_global_memory_reads(std::size_t count, std::string column_name = {}, base b = base::TEN)

or

enum class bytes { BASE_TWO, BASE_TEN };
template <typename ElementType>
void add_global_memory_reads(std::size_t count, std::string column_name = {}, bytes b = bytes::BASE_TEN)

The latter may be clearer at the call site:

state.add_global_memory_reads<nvbench::int32_t>(num_values, "DataSize", base::TEN);
// vs
state.add_global_memory_reads<nvbench::int32_t>(num_values, "DataSize", bytes::BASE_TEN);

And we could make it a template parameter instead in order to avoid forcing specifying a name in order to specify the base:

enum class bytes { BASE_TWO, BASE_TEN };
template <typename ElementType, bytes B = bytes::BASE_TEN>
void add_global_memory_reads(std::size_t count, std::string column_name = {})
...
state.add_global_memory_reads<nvbench::int32_t, bytes::BASE_TEN>(num_values);

I'll defer to what @allisonvacanti thinks is best here.