* fixup: check for env variables based on go env
not all golang env specific variables are
injected into vim.env, so check their presence
based on go env instead
* prevent emtpy lines at the end of go build
* fixup: treat empty values as nil
1) count the overall test coverage per-file and per-project
2) add gotestsum as a test runner option
3) handle windows GOPATH and
4) minor fix: stop GoFmt if no formatter is available