Add a snippets folder

The snippets folder is not tracked; it stores code to play with data or
might come handy.
Add a dbus_data folder

Data from Dbus (transit agency that serves San Sebastian, Spain) is very
good for training, as the data frequency is very high. It is
unfortunately not public. 

I use this folder to track the queries that I run in our PostgreSQL
server to create training and test datasets.

Results of the queries are saved as csv files, which is not tracked
(size too large).
Add a literature folder

In this folder there is a representative (although not complete) list of
papers on the topic of bus arrival prediction.