ci: Update GoReleaser and other actions.

Fix type when indexing Go string.

Recognize signal.h header.

deps: update cc/v3

libc: safer realloc implementation

deps: switch to go1.18

Signed-off-by: Rui Chen <[email protected]>

cxgo: do not flatten blocks with decls; fixes #42

test: always wait for all goroutines

docs: update the readme

ci: configure goreleaser