Financejson

Fixes
The financial data related to trends (index trends, industry trends,...) require a period to date conversion that lead to non-unique indices when saving data to databases using the [FinDataBroker](https://github.com/tomerten/findatabroker/) package.
These issues should now be fixed.

Beta release
Updated some issues with required fields in the JSON schema and adapted unit tests accordingly.

Updates
Resolved issues with licence link in readme file.

Schema updates
The schema has been updated to include an index_symbol, to facilitate easy saving and loading to/from SQL databases. For the same reason, required fields have been introduced to allow the building of SQL indices for each data field.

V1.0.1-valpha.3
Updates
JSON schema updated such that each value is a list of dicts. This makes the schema more consistent and allows to reduce the code for the [FinDataBroker](https://github.com/tomerten/financejson/blob/master/FinDataBroker) package.

V1.0.1-valpha.2
Updates
JSON schema updated such that each value is a list of dicts. This makes the schema more consistent and allows to reduce the code for the [FinDataBroker](https://github.com/tomerten/financejson/blob/master/FinDataBroker) package.

First release