Bump version to 5.1.0 #174

Job	Run time
check / clang-checks	1m 42s
check / editor-config	11s
build-os-matrix	4s
build (oraclelinux:9) / build	2m 2s
make-tests (oraclelinux:9) / tests	1m 50s
rpm-build (oraclelinux:9) / rpm-build	5m 47s
rpm-install (oraclelinux:9) / rpm-install	1m 14s
	12m 50s

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