Pdal-plugins

* Do not override CMAKE_BUILD_TYPE
* CI fixes
* Explicit casts of integers for streams being passed between PDAL/Python

**Full Changelog**: https://github.com/PDAL/python-plugins/compare/1.2.0...1.2.1

* Require PDAL 2.4.0
* Set CMake project name to pdal-python-plugins

* PDAL 2.4+ now required, along with C++17
* Updated nlohmann JSON library
* Dropped 3.6 Python support

* automated release push

* auto-release run-through

* Initial move of `filters.python` and `readers.numpy` from PDAL Python package to their own package.