Normalize values and units on all exporters

[nickbabcock]

After implementing #67 to conform to prometheus best practices, I'd like to apply that PR to the other exporters. I want:

• One type to represent number of bytes. SmallData (2^20) and Data (2^30) should just become bytes, so that one doesn't need to lookup source code to figure out how to convert them to bytes.
• One type to represent frequency (Hz). Frequency (Hz) and Clock (MHz) should be consolidated into hertz. Clock is annoying in grafana as there isn't a native MHz unit, so one has to multiply values by 1000000 before mapping to Hz.
• All exporters to be consistent in the data they are exporting

I haven't decided yet if the other exporters should adopt the more descriptive names like prometheus (eg: prefer "bytes_per_second" over "Throughput"), so I'm unlikely to act on this issue immediately.

I think any solution will require the use of a config field like normalize_units that will be enabled by default. That way new installations will, by default, use the improved units and values, while ongoing installations can opt into preserving their desired behavior