Switch Smartermeter::Samples to parse data to UTC.

Previously dates were reference in local time which meant if it was
executed in different timezones it would yield different results. In
order to clarify, now all dates are referenced based on UTC.
A more idiomatic way to sum an array.
Update the pachube spec.
Add rdoc for ruby 1.8.7 compatibility.
Drop 1.8.7 support
Revert "Add rdoc for ruby 1.8.7 compatibility."

This reverts commit 785ec4715dd089cf01c0334b22106fe54cfb02cc.
Change Samples to be an Array instead of Hash

In order to better accommodate timezones, we no longer store data in
Hash as it can change depending on the perspective of the accessor.
There is now a new method #on which takes a DateTime object, which
allows for the specification of a timezone and it includes all samples
from the given input, till 24 hours into the future.
Merge pull request #28 from mcolyer/mc-samples-in-utc

Switches samples to UTC