Ecole

New features
- Make `libecole` a installable CMake library (no Python). 240
- Refactor Ecole packaging to allow the creation of [Ecole Python extensions](https://github.com/ds4dm/ecole-extension). #282
- Add method to reactivate SCIP logger. 283
- Added possibility use SCIP default in `Branching` environment by passing `ecole.Default` 294 303

Bug fixes
- Normalized edge coefficients in node bipartite observation. 270
- Fix difficulty of instance generators 301

Breaking changes
- Change StrongBranching `pseudo_candidate` parameter default value. 239
- Observations functions now use uniformly variable indices (instead of LP). In most cases, this will not impact user code. 210
- Remove deprecated functions/emum `NodeBipartiteObs.column_features`, `NodeBipartiteObs.ColumnFeatures`
- Rename `RandomEngine` to `RandomGenerator`
- Renamed exceptions to `ScipError` and `MarkovError` 302
- Move to SCIP8 on Conda-forge 303

Bug fixes
- Add constructor option to extract only LP branching candidates in `Kalild2016` (default behavior is changed to match that of the `Branching` environment).

Bug fixes
- Reward / observation extraction is now made in the proper order in both the C++ and Python Environment class
- Observations are not extracted twice any more in the Python Environment class (bug introduced in v0.7.0)

Bug fixes
- Fix discrepancy between Ecole build-time version for libfmt (fmt7) and the conda package dependency version for libfmt (fmt8)

New features
- Add a `FileGenerator` to iterate over local problem instances 174
- Add `Hutter2011` observation function 192
- Add `PrimalIntegral`, `DualIntegral`, `PrimalDualIntegral `reward functions 144
- Add `BranchingSum` multi-variable branching environment 181
- Add `PrimalSearch` environment 183
- Terminal states (`done==True`) always return `None` as an observation 199
- Rewards are now extracted before observations, to account for the observation extraction cost between two rewards 212

Bug fixes
- Fixed a bug in `IndependentSetGenerator` where the greedy clique strengthening was not as greedy as it should.
- Documentation typos

Bug fixes
- Fix invalid `NodeBipartite` when constraint had both lhs and rhs 189