Geofileops

In this release, the main change is a new operation that has been added: nearest_join.

Improvements:
* 12: new operation nearest_join().
* 14: improve performance for files where the rowid isn't consecutive.
* Improve documentation, mainly for the select operations.
* Add check in get_layerinfo on column names containing illegal characters (='"').
* Suppress fiona warning "Sequential read of iterator was interrupted."
* Dissolve: output is sorted by a geohash instead of random, which improves performance when reading the file afterwards.

Changes that break backwards compatibility:
* Drop support for spatialite < 5 and geopandas < 0.9.
* Bugfix: for the dissolve operation, when rows in the groupby columns contained NULL/None/NaN values, those rows were dropped. This is the default behaviour of (geo)pandas, but as the behaviour doesn't feel very intuitive, it was decided to divert from it.

Improved performance for all operations that involve overlays between 2 layers (intersect, union, split,...).

Improvements:
* Improved performance for all operations that involve overlays between 2 layers (intersect, union, split,...). Especially if the input files are in Geopackage format the improvement should be significant because in this case the input data isn't copied to temp files anymore.
* Added the method geofile.execute_sql() to be able to execute a DML/DDL sql statement to a geofile.
* Smaller code cleanups to improve readability on several places.

Bugfixes:
* In the split and union operations, in some cases (mainly when input layers had self-intersections) intersections in the output were unioned instead of keeping them as seperate rows.
* When using an input file with multiple layers (eg. a geopackage), this sometimes resulted in data errors.
* Fix an error in the lang simplification algorithm that occured in some edge cases.

This release mainly brings improvements and bugfixes when using the Lang simplification algorithm.

Additionally, this is the first version that gets a conda package.

Improvements:
* Support for all geometry types for Lang simplification
* Some code restructuring + code cleanup in util (backwards compatible for now, but isn't public interface anyway)
* Improve test coverage

Bugfixes:
* preserve_topology wsn't always respected in Lang simplification
* clip_on_tiles =False in dissolve resulted in some polygons not being dissolved. Because there is no easy solution, parameter is deprecated and always treated as True.

This release is mainly focused on improvements to the dissolve and simplify operations.

It is important to note that for the dissolve operation the default parameters behave slightly different, so the change is not backwards compatible!

Most important changes:
* Dissolve
* Different handling of default parameters (not backwards compatible!)
* Better performance
* Several bugfixes
* Simplify: add support for different simplification algorythms: ramer-douglas-peucker, visvalingam-whyatt and lang.
* Many improvements to documentation
* Improvements to type annotations
* Some new undocumented (so use at own risk!) functions were added to geofileops.vector_util.
* simplify_ext: an "extended" simplify function:
* Supports multiple simplification algorythms: ramer-douglas-peucker, visvalingam-whyatt and lang.
* Option to specify a "points-to-keep geometry": points/nodes of the geometries to be simplified that intersect it won't be removed by the simplify operation.
* count_number_points: count the number of coordinates that any shapely geometry consists of

This version contains quite some fixes and small improvements. The most important ones are listed here.

Improvements:
* Stop using sqlite WAL output format as default: gives locking issues when using files on a file share
* Improve handling of output geometry type
* Add scripts, dependencies,... to use pytest-cov to report unit test coverage
* Add first version of sphynx documentation
* Improve test coverage
* Improve benchmark tests

Fixes:
* Negative buffer shouldn't output rows with empty geometries
* Dissolve gave an error in some specific cases
* Join_by_location operation gave wrong results

Most typical operations are now supported: buffer, simplify, export_by_location, intersect, union, erase, dissolve,...