really don't use github_api_config and github_api_host
Merge branch '466-github-api' into 466-github-api-old
Revert "really don't use github_api_config and github_api_host"

This reverts commit 1b7fe41bbb9493faeab78a4a4a16f3ef12157955.
refactor: extract function github_api
allow installing the latest GitHub release by passing release = TRUE to, or using the syntax "user/repo@*" in install_github
update NEWS
supply test
Roxygenize
fix comment