Add manuscripts2 containing new functions to calculate the metrics

- new_functions.py: contains Query & Index classes and functions
to parse the fetched data
- derived_classes.py: contains PullRequests and Issues classes
- Readme.md describing how to use the above 2 files
- tests for the basic functions inside the Query class

Also add:
- Examples/Sample_metrics.ipynb: contains the CHAOSS and GMD
metrics that are being calculated using the new functions

Addresses issues chaoss#59 and chaoss#62