DOC Update to v0.13

DOC Update to v0.12

Merge pull request #180 from rapidsai/taureandyernv-patch-6

Update CONTRIBUTING.md

Update CONTRIBUTING.md

Added clear directions to update readmes

Delete Dask_with_cuDF_and_XGBoost.ipynb

Update NYCTaxi-E2E.ipynb

cleaned up output, minor fixes

Update README.md

added blog link to Taxi notebook

Added blogs to Kaggle on Readme

Added Santander and kaggle blog links, and updated

Update census_education2income_demo.ipynb

updated MSE and CoD code due to api changes

Update GTC_tutorial_student.ipynb

updated values for train and test