Upgrade all dependencies & enforce action.type

[JaKXz]

• action.type must be a string or Symbol (the latter may or may not be
  dropped, so test support can also be removed easily)
• use npm scripts instead of Makefile
• use Babel 6. Closes when to update to babel6 ? #25.
• use nyc (disclaimer: I'm a collaborator on nyc) for code coverage and coveralls
• test against latest versions of Node LTS
• add .editorconfig
• use mocha.opts and mocha-friendlier file structure [+this way __tests__ are not published in the npm package]
• fixes minimatch dependency warnings [from mocha 2.x and babel 5.x]
• specify package files in package.json files to reduce published lib size
• use cross-platform-friendly commands with cross-env and rimraf
• add yarn.lock 🎉

@acdlite @yangmillstheory I got a little carried away (when I noticed iojs in .travis.yml)... hopefully all of this makes sense - apologies for all of it at once.

[JaKXz]

CI is was failing only because npm@2 doesn't like unresolved peer dependencies and eslint-plugin-airbnb-base hasn't updated its peerDependencies, yet: airbnb/javascript#1101

[acdlite]

@JaKXz Sorry I haven't responded to this yet! Been pretty busy lately. This all looks great.

[JaKXz]

@acdlite no worries! life first 👍

I'll reset my last commit.

[acdlite]

Btw I just sent you an email