Add error handling notes.
A script to generate test data.
Add custom exception file.
Modify insert_reading, so timestamps can be included in the data.

Also, fix the exception error handling.  It did not do anything before.  Now it will throw an exception when one tries to insert for a timestamp that already exists (date_entered is the model field).
Merge branch 'optimize' of github.com:visgence/portcullis into graphOpt