Ecole

New features
- Add PyPI source package 185 37

New features
- Add MilpBipartite observation function for pre-solving (147)
- Add Pickle support to all observation functions (106 152)
- Features description for `Khalil2016` (157)

Breaking changes
- `NodeBipartite` features have been reordered
- Changed combinatorial auctions, maximum independent set and capacitated facility location instance generators so that they produce instances of difficulty similar to those of Gasse et al. (2019) out-of-the-box (141, 142 150)
- `Khalil2016` now returns a struct wrapping the Numpy array (157)

Bug fixes
- Fix performance bottleneck in `Khalil2016`
- Improve Python detection in source (venv) builds 133

New features
- Add enum to `NodeBipartite` to describe feature columns.
- Add `Khalil2016` observation function.
- `SolvingTime` rewards are now given in seconds (used to be miliseconds).
- Move instance generators from Python to C++
- Source build automatically download libraries if they are not found (except for SCIP) without Conan
- Ecole automatically builds with [IPO](https://en.wikipedia.org/wiki/Interprocedural_optimization) when available and [`xsimd`](https://github.com/xtensor-stack/xsimd)

Bug fixes
- Finishing partial fix of 98

Bug fixes
- Fix bad handling of SCIP limits 98