feat: Add C API header #134

Job	Run time
Settings / settings	3s
Lint / Lint	13s
Official Docker image / Build	1m 5s
Test Linux distros / Matrix configuration	5s
Build docs / Build docs	38s
Build and test / Matrix configuration	7s
Test Linux distros / Alpine	13m 50s
Test Linux distros / ArchLinux	12m 37s
Test Linux distros / CentOS	13m 11s
Test Linux distros / Debian	11m 17s
Test Linux distros / Fedora	10m 48s
Test Linux distros / OpenSUSE	11m 5s
Test Linux distros / Ubuntu	12m 28s
Build and test / linux x64 Debug static	11m 39s
Build and test / linux x64 Debug shared	11m 50s
Build and test / linux x64 Release static	12m 34s
Build and test / linux x64 Release shared	12m 17s
Build and test / osx x64 Debug static	10m 28s
Build and test / osx x64 Debug shared	13m 1s
Build and test / osx x64 Release static	13m 16s
Build and test / osx x64 Release shared	16m 12s
Build and test / osx arm64 Debug static	6m 24s
Build and test / osx arm64 Debug shared	6m 57s
Build and test / osx arm64 Release static	7m 16s
Build and test / osx arm64 Release shared	6m 36s
	3h 35m 57s

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