This update now uses go mod and requires 100+ dependencies to build.
Quite sad for a simple system value collector. Also the amd64 version
does not correctly report the memory used by the buffer cache. This
is a defect from building OpenBSD/amd64 binaries without cgo.
This no longer uses promu for builds but passes the same build vars
to go build via MODGO_LDFLAGS.
With help and OK sthen@ abieber@
639dff41be