More parameters for optimization

You can now pick specific expected return and risk models. Here is a list of the ones you can use:

Expected return

• mean_historical_return

• ema_historical_return

• capm_return

Risk model

• sample_cov

• semicovariance

• exp_cov

• ledoit_wolf

• ledoit_wolf_constant_variance

• ledoit_wolf_single_factor

• ledoit_wolf_constant_correlation

• oracle_approximating