Add some more commands for installing/removing/listing versions

[urso]

• Package github.com/anrewkroh/gvm acts as a library now. One can use gvm.Manager for writing custom tools.
• Versions are parsed now. E.g. one can use version 1.11beta1 or 1.11-beta1 to download the go 1.11 beta1 release. The version formatter ensures the correct file is found for downloading.
• Moved CLI to github.com/anrewkroh/gvm/cmd/gvm
  • Add support for new commands:
  • use: implements old behavior. Install and write CLI settings to stdout
  • install: download binary version
  • available: print list of installable go releases
  • list: list all installed versions
  • remove: remove some versions
  • purge: remove all but latest stable/unstable version
  • Default command is use. CLI can be used as before

[andrewkroh]

I get an error when running available on mac and win. Everything else works as I would expect.

$ ./gvm available
gvm: error: Get /Users/akroh/.gvm?marker=: unsupported protocol scheme ""

PS C:\Gopath\src\github.com\elastic\beats> .\gvm.exe available
gvm: error: Get c:\Users\vagrant\.gvm?marker=: unsupported protocol scheme "c"

[andrewkroh]

I working on adding AppVeyor BTW. There's something wrong with my account and I can't add or remove any project so it's going to take a bit b/c I need to contact support.