Support multiple install methods for a single binary

[kzantow]

In order to make more flexible binny configurations, while remaining performant, it would be useful to support multiple installation methods.

An example that needs this is: installing gh on FreeBSD. Today, there is no binary published for FreeBSD, so a user would need to use the go-install method for portability. However, the go-install method is slow since it needs to download all dependencies and run a complete go build. It would be preferable to attempt to download a binary using the github-release method, and if that failed to fall back to a go-install.