Clarify aggregation output structure

• add second example which illustrates the output of the aggregation
• add the second publication about storage modeling in readme
• modify usable attributes to properties

v0.9.4

• Improvement of extreme periods
• Move to MIT license

v0.9.3

Patch to first public version with minor bug fixes

v0.9.2

First public release

Features:

• different aggregation methods implemented (averaging, k-mean, exact k-medoid, hierarchical), which are based on scikit-learn or pyomo
• flexible integration of extreme periods as own cluster centers
• weighting for the case of multidimensional time-series to represent their relevance

v0.9.1

First public release of tsam