Error when UnBlendedCost is missing

[syphernl]

For a new environment we've set up billing reports (aws-billing-detailed-line-items-with-resources-and-tags) but the CSV's generated don't seem to have any of the (un)blended rates or cost yet this library assumes it is there.

As a result, traceback is generated:

Traceback (most recent call last):
  File "./analyse.py", line 19, in <module>
    total = details.load(options.filename)
  File "/home/frank/.local/lib/python2.7/site-packages/details/__init__.py", line 36, in load
    data['UnBlendedCost'] = decimal.Decimal(data['UnBlendedCost'])
KeyError: 'UnBlendedCost'