v0.2.0

Added Oracle LEACE implementation (#2) which achieves even more surgical edits than standard LEACE when ground-truth concept labels are available at inference time. The classes OracleFitter and OracleEraser are designed to work almost exactly like LeaceFitter and LeaceEraser except that OracleEraser requires an extra z positional argument in its forward method.

This release also fixes a subtle bug in our covariance matrix shrinkage implementation which caused NaN results when the data has zero variance (#3).