add more detailed QA checks for license info

[ha0ye]

Extending the problem in #10, sometimes license information exists, but which is not readily available through the GitHub API.

For example, https://github.com/cran/disco is a mirror of disco package in the CRAN R package repository, and the DESCRIPTION file indicates a GPL license. But because this does not follow github convention of a LICENSE file, the GitHub API does not return any license information.

Adding additional check to the R script to retrieve license info could help deal with this corner case. (and other additions to handle other corner cases)