Fix Glibc errors

[jdmcd]

Fixes #21. Thanks for the help, @vzsg!

[vzsg]

Erm. Hi. I didn't expect my fork to show up like this.

Some explanation about the changes:

• Swift 4.2 allows us to declare system libraries inside the project, without needing a separate dependency repo. That's what the first commit is about, dropping CSSH.
  But it's a breaking change for the package.
• The second commit is the more important thing for the issue @mcdappdev is experiencing: installing Shout along with SwiftNIO causes a symbol clash, and prefixing the constants with Foundation. fixes that. You might want to cherry pick that in nevertheless.

[jakeheis]

I think I'd like to get one more version of Shout out that supports Swift 4.0, so if this PR could be split into two -- one that fixes the symbol crash, and one that updates Package.swift to use the new system libraries feature -- that would be ideal

[jdmcd]

Agreed, that sounds like a good plan. I don't have much bandwidth the next week or so as I'll be mostly offline but I can loop back on this after. Thanks, Jake!

[vzsg]

Check out #22. The other part is completely optional, and you can salvage the target setup from gotranseo's or my fork later if you want.

[jdmcd]

Perfect, I’ll close this for now then. Thanks @vzsg!