Add support for rust-based extensions #103

Job	Run time
prepare	7s
build / Generate matrix	24s
build / Linux (linux_amd64, ubuntu:18.04, x64-linux)	8m 0s
build / Windows (windows_amd64, x64-windows-static-md)	20m 36s
build / MacOS (osx_amd64, x86_64, x64-osx)	1m 58s
build / DuckDB-Wasm (wasm_mvp, wasm32-emscripten)	1m 58s
build / Linux (linux_amd64_gcc4, quay.io/pypa/manylinux2014_x86_64, x64-linux)	4m 28s
build / Windows (windows_amd64_rtools, x64-mingw-static)	39m 4s
build / MacOS (osx_arm64, arm64, arm64-osx)	1m 33s
build / DuckDB-Wasm (wasm_eh, wasm32-emscripten)	1m 51s
build / Linux (linux_arm64, ubuntu:18.04, arm64-linux)	8m 16s
build / DuckDB-Wasm (wasm_threads, wasm32-emscripten)	1m 56s
doc_test / docs	13s
deploy	0s
docs_all	0s
	1h 30m 24s

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