Pypsa

**New Features**

* Linopy now uses [highspy](https://pypi.org/project/highspy/) as an interface to the HiGHS solver. This enables a direct and fast communication without needing to write an intermediate LP file.

**New Features**

* The function `LinearExpression.from_tuples` now allows `ScalarVariable` as input.
* For compatibility reasons, the function `groupby_sum` now allows `pandas.Series` as input.

**Bug Fixes**

* Filtering out zeros is now an optional feature in the `solve` function. The previous behavior of filtering just before the LP file writing, lead to unexpected errors for constraints with only zero terms.

**New Features**

* A new module was created to export basic mathematical quantities such as `lb`, `ub`, `c` vectors and the `A` matrix. Use it with the `matrices` accessor in `linopy.Model`.
* For `Constraints`` and `Variables`` a `ipython` autocompletion function for getting items was added.
* Inplace updates for constraints are now more flexible.
* AnonymousConstraint can now built from comparison operations of variables with constants, e.g. `x >= 5`.
* The `Model.add_constraints` function now support input of type `ScalarVariable`, `ScalarLinearExpression` and `ScalarConstraint`.
* Terms with zero coefficient are now filtered out before writing to file to avoid unnecessary overhead.
* The function `sanitize_zeros` was added to `Constraints`. Use this to filter out zero coefficient terms.

**Bug Fixes**

* Solving with `gurobi` and `io_api="direct"` lead to wrong objective assignment if the objective contained non-unique variables. This is fixed in this version.

This release introduces new features related to expression creation and comes with an improved documentation.
Due to some indexing bugs in the latest xarray package `v2022.06.`, the xarray depedency was fixed to maximally `v2022.03.`

See [release notes](https://linopy.readthedocs.io/en/latest/release_notes.html#version-0-0-10) for details.