Packaging and build systems

[mgree]

~~Things are a disaster. I have to unset SDKROOT when on macOS to get a build to work. (But I need it set to get Haskell to work.)~~

Ideally we should have:

• [x] opam package for libdash
• [x] change .travis.yml to actually build things rather than use Docker
• [x] build on multiple OSes
• [x] ~~make -j4 or something, i mean come on~~ breaks lem and maybe us too?
• [ ] add back Modernish tests
• [x] change to just depend on an opam package for lem
• [x] build uses lem OPAM package, submodule removed
• [ ] opam package for smoosh
• [ ] build just uses these packages (with local pinning?)
• [ ] have a Travis build that actually tests Docker (and Vagrant, too?) best approach: use OPAM!
• [ ] log test output and post somewhere meaningful (run other shells, too? or is all this a separate repo?)