Terracotta

What's Changed
* Add transparency mask support for /compute by dionhaefner in https://github.com/DHI-GRAS/terracotta/pull/222
* optimize_rasters: skip_existing by chapmanjacobd in https://github.com/DHI-GRAS/terracotta/pull/224
* Require pymysql>=1.0.0, which has a context managed connection by nickeopti in https://github.com/DHI-GRAS/terracotta/pull/229
* Use Flask error handlers instead of decorators (74) by nickeopti in https://github.com/DHI-GRAS/terracotta/pull/227
* fix docs by dionhaefner in https://github.com/DHI-GRAS/terracotta/pull/231
* Introduce multiqueries for dataset lookup 33 by nickeopti in https://github.com/DHI-GRAS/terracotta/pull/230
* Parallel raster optimisation by nickeopti in https://github.com/DHI-GRAS/terracotta/pull/228
* Allow CORS from localhost by default (197) by dionhaefner in https://github.com/DHI-GRAS/terracotta/pull/236

New Contributors
* nickeopti made their first contribution in https://github.com/DHI-GRAS/terracotta/pull/229

**Full Changelog**: https://github.com/DHI-GRAS/terracotta/compare/v0.7.2...v0.7.3

Fixes a bug that made `TC_EXTRA_CMAP_FOLDER` unusable.

New features

- A whole new and shiny preview app in React (thanks to bertearazvan).
- `terracotta ingest` now has a `--skip-existing` option.
- Use of multiprocessing is now configurable via `TC_USE_MULTIPROCESSING`.

Bug fixes

- Automatically respawns broken process pools.
- Better MySQL caching and URL parsing.
- Bumped dependencies.

We added support for custom color maps and fixes to the raster driver and the MySQL database driver

Changes

* You can now conveniently include your custom color maps in an `EXTRA_CMAP_FOLDER` of your choosing, thanks to dionhaefner
* Rasters with existing alpha bands now just work (176) fixed by dionhaefner
* `/colormap` response changed: JSON key is called `rgba` instead of `rgb` and contains 4 values.

Bug fixes

* MySQL database driver getting into broken state limbo is now prevented (174), by j08lue and dionhaefner

Other

* Docs now rst-magically build the color map visualizations and got rid of their Matplotlib dependency, by dionhaefner

This release contains some critical bug fixes and quality-of-life improvements.

Changes
- The config parameters `UPSAMPLING_METHOD` and `DOWNSAMPLING_METHOD` are now `REPROJECTION_METHOD` and `RESAMPLING_METHOD`, with different semantics.

Bug fixes
- As it turns out, retrieving tiles with GDAL is not thread-safe. Therefore we now use multiprocessing (on systems where it is supported) to retrieve the three RGB bands in parallel.
- Terracotta's default transform failed to produce meaningful results in certain edge-cases. We thus reverted to GDAL's default transform, but with the additional feature that tiles never undersample the original dataset. This seems to give good performance both for high and low zoom levels.

Other
- Some tweaks to the docs by YuhangCh and j08lue.
- CORS is now configurable thanks to j08lue.

No big changes, just some tweaks and bug fixes that accumulated during the last couple of months.

Bug fixes:
- Adapt to recent library versions
- Do not use `GDAL_DISABLE_READDIR_ON_OPEN` anymore (139)
- `cache_cluster_ttl` in `zappa_settings.toml.in` is now an integer

Other:
- Now tested with Python 3.8