0.2 Alpha release of the Leontief library for EEIO calculation

The first release lays down the basic shape of the Leontief library. Includes a number of examples both from IO and SUT systems, both working with real data and stylized calculations and algorithms.

There is a testing framework and documentation in place within the repository. User oriented documentation will developed here and in due course Academy courses.

The classes and API will evolve to improve usability and expand the range of functionalities.