Provide standard conversions

[amorphic]

Netmeasure measurements always returns result values in the highest precision units possible. This allows the user to decide whether or not to convert to a lower precision unit.

However it would be nice is users had a standard means to convert between units of a particular type (Network, Storage, Time) so that:

1. They didn't have to reinvent the wheel
2. There was less chance of mis-conversion

This card will be complete when functionality exists to convert between units of a particular type.