Lot of manifests are using github tags to find the latest version the
url's and regex is mostly the same.
`checkver` now can also be the string "github" if the `homepage` links
to the github repo
If `homepage` is not the repo `{"checkver": "github":
"https://github.com/user/repo"}` can be used
* The default location of the secret key was changed to ~/.minisign/minisign.key.
* Generating a new set of keys (-G) doesn't replace an existing key pair any more; the additional -f switch is required in order to force this operation.
* Improved error messages and Windows compatibility.
* A man page was added.
