Unit test framework

Each algo code should be easily unit tested. The concept of unit test is not very known to the type of users here. Rather than asking them to build their own unit test, we should provide some high level template that does:

- provide local fake backend
- provide fast replay executor
- use real (past) market data
- with a pre-defined small set of symbols, simulate a (constant) day using the historical data quickly, basically smoke test to catch any issues like typo.