Don't trust GitHub to identify repo's primary language

[y]

The formula should not only looks at the language that GitHub thinks is the primary language, but should look at all languages identified in the repo. The Pithub API shows that there is a way to examine all languages for a repo.

A few examples where this matters: GitHub frequently misidentifies XS modules as C; and if there's JavaScript included in a repo, GitHub can identify the primary language as JavaScript if it has more lines of code. To avoid this issue, all the languages for a repo should be examined to see if Perl occurs in the list and not just as the primary language.

(This was initially posted as a comment to #2, but apparently went unnoticed.)