Fix case inconsistencies in imports

[reesmichael1]

After running nimble install feednim, I was unable to actually import FeedNim into my project:

/home/reesmichael1/.nimble/pkgs/FeedNim-0.2.1/FeedNim.nim(3, 15) Error: cannot open file: feednim/atom

This was because FeedNim.nim was importing from feednim (instead of FeedNim). This pull request fixes the case inconsistencies.

Thanks for a really nice library!