Pylandstats

- cell width and length comparisons with `numpy.isclose` to deal with imprecisions that come from float pixel resolutions (e.g., in GeoTIFF files)
- critical fix: moved pythran signatures from `compute.pythran` to `compute.py` so that the build is properly done when pip-installing

- flat array approach to the computation of the adjacency matrix with pythran to improve performance (plus fixes a bug on the computation of `total_edge`)
- initialization of `scipy.spatial.cKDTree` with keyword arguments `balanced_tree` and `compact_nodes` set to `False`

- methods plotting multiple axes return only the figure instead of a tuple with the figure and the axes
- settings module that allow configuring metrics' labels in plots, defaulting to FRAGSTATS abbreviations
- chaged CRS in tests to work with pyproj >= 2.0.0
- corrected `figlength` for `figwidth`
- warn when computing metrics that require an unmet minimum number of patches or classes (and their computation returns nan)
- all tests with `unittest.TestCase` assert methods

- added docstrings for `MultiLandscape`, `GradientAnalysis` and `BufferAnalysis`
- raise `ValueError` when using buffer rings around a polygon geometry

- implemented `SpatioTemporalBufferAnalysis` with a dedicated `plot_metric` method
- added buffer ring-wise analysis through a `buffer_rings` boolean argument in `BufferAnalysis`

- float equality comparations with numpy `isclose` method