Merge pull request #42 from andrewwhitehead/fix/ffi-usize #56

Job	Run time
Run checks (ubuntu-latest)	4m 38s
Run checks (macos-latest)	5m 35s
Run checks (windows-latest)	14m 14s
Run tests (ubuntu-latest)	8m 11s
Build library (linux-aarch64, ubuntu-latest, libindy_credx.so, aarch64-unknown-linux-gnu, true)	6m 3s
Run tests (macos-latest)	9m 47s
Build library (linux-x86_64, ubuntu-latest, libindy_credx.so, x86_64-unknown-linux-gnu, true)	7m 0s
Run tests (windows-latest)	18m 48s
Build library (darwin-universal, macos-latest, libindy_credx.dylib, darwin-universal, beta)	10m 54s
Build library (windows-x86_64, windows-latest, indy_credx.dll, x86_64-pc-windows-msvc)	11m 48s
Build and test Python wrapper (linux-aarch64, 3.8)	29s
Build and test Python wrapper (linux-x86_64, 3.8)	24s
Build and test Python wrapper (darwin-universal, 3.8)	39s
Build and test Python wrapper (windows-x86_64, 3.8)	53s
	1h 39m 23s

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