Add tests that nodes are correctly extracted in FunctionReporter

[jameslamb]

In test-FunctionReporter, we should add tests confirming that pkgnet correctly translates package exported namespaces to nodes.

[bburns632]

I believe THIS TEST on baseballstats confirms that a node is created for each function within the package.

However, if someone has a suggestion on how we can make this testing more robust, especially on edge case R package designs, please feel free to comment here.

[jayqi]

This issue is maybe too open ended. In any case, I have new tests in #181 checking the whole extracted network for all three of baseballstats, sartre, and milne. I think this should be good enough, and if we identify new edge cases, we should introduce them to those test packages or as new test packages as needed.

https://github.com/UptakeOpenSource/pkgnet/pull/181/files#diff-672ae504c307217ca3f5678b6473fdd6