Update to Elm 0.18

[Anahkiasen]

I didn't find a CONTRIBUTING.md so I tried to update the repository the best I could.

Few things to note:

• Latest version of elm-test already comes with a Node runner so I removed the manual compilation to JS
• There were two or three ways the tests seemed to be runnable from: npm test, make test there was also a prepare_test file, so I got a bit confused. I tried to streamline the process the best I could with what the tools allow in their latest versions
• I tried to run elm-format on the repository to cleanup my changes but the latter formats to 4 spaces as indentation instead of the 2 configured here so I thought it best to not touch that part
• I wasn't sure what to do with Http.decodeUri (and encode) now returning Maybes. I've just added a basic Maybe.withDefault "" where relevant but you may have a better way
• A lot of things changed in elm-test generally, I've tried to update the test suite in a way that made sense but I think it could be cleaned up way more – I'm new to Elm but it appears a lot of the things you did manually (generating test suites and stuff) is now handled built-in by elm-test so, might want to take a look at it
• I saw a CI badge in the README but no CI configuration file nor automated validation of pull requests so, not sure what to do on that part

[sporto]

Great, thanks for this