Multiple measures for aggregation.
Add Sherlock-comments to most aggregation methods (since it's complex) and fix a minor irritation (default values of parameters)
This fixes #681 on github.
Remove German comment.
It says that someone (GKA) said yes is no in Russian (almost no in Russian is нет).
TEST CHANGE! and tests added.
Since AggregateParamParser now returns a list of measures instead of a single measure tests need to be modified accordingly.
Also added tests for multiple measures.
Fix typos found in code review.
Merge pull request #682 from openspending/681-multiple-measures

681 multiple measures