Pylandstats

- implemented `GradientAnalysis` and `BufferAnalysis`
- added optional `geopandas` dependences
- created abstract `MultiLandscape` class
- `Landscape` initialization from ndarray or geotiff (dropped `read_geotiff` method)
- implemented `contagion`
- convolution-based adjacency dataframe
- fixed bug with `class_cond` in `Landscape.compute_arr_edge`

- implemented `euclidean_nearest_neighbor` and all its corresponding class/landscape distribution statistic metrics
- fixed dtype of `self.classes` in `landscape.Landscape`
- set default argument `nodata=None` (instead of `nodata=0`) for `landscape.read_geotiff`
- changed test input data files
- implemented `__len__` of `spatiotemporal.SpatioTemporalAnalysis`

- corrected if-else statements involving `None` variables

- initial release
\[v3.0.0\]: https://github.com/martibosch/pylandstats/compare/v3.0.0rc2...v3.0.0
\[v3.0.1\]: https://github.com/martibosch/pylandstats/compare/v3.0.0...v3.0.1
\[v3.0.2\]: https://github.com/martibosch/pylandstats/compare/v3.0.1...v3.0.2
\[v3.0.3\]: https://github.com/martibosch/pylandstats/compare/v3.0.2...v3.0.3