* Problem: Amount error is not tested on the HTTP level.
Solution: A failed web test to reproduce the problem.
* Problem: Invalid transaction posted to Tendermint
Solution: Pass the exception to HTTP POST handler function
* Problem: DoubleSpend and CriticalDoubleSpend not differentiated
Solution: Handle these exceptions differently in `get_spent`
* Problem: No test for checking exception DoubleSpend and CriticalDoubleSpend
Solution: Add necessary tests
* Problem: find doesn't raise IndexError
Solution: Remove exception handling for IndexError
* Problem: Upsert validator not migrated to Tendermint 0.19.0
Solution: Migrate the same to Tendermint 0.19.0
* Problem: There are no tests for public key encoding/decoding
Solution: Add necessary tests
* Remove testing for rethinkdb, mongodb, and Py3.5
* Add first tests
* Add validation
* Add command to start the ABCI Server
* Reuse existing MongoDB Connection class
* Use DuplicateTransaction
* Test only tendermint
* Update travis scripts
* Fix pep8 errors
* Update Makefile
Vanshdeep Singh
Shahbaz Nazir
Sylvain Bellemare
vrde