Financial-analysis

Fix the set_freq function and add some functionality:

- forward fill when upsampling
- use `method` parameter of the `asfreq` method in `set_freq`
- test cases for `set_freq` module

- remove reading of requirements from files and use direct list instead

- `limit-order-book` is not required

- add `log_return` parameter to the cash_returns method

Calculations of:
- cash return
- percent return
- volatility