lint support for our syntax

Nobody has claimed this yet.

Problem `foo::bar()` is marked as an parsing error by eslint's esprima parser.

We should can plugin a custom parser that behaves like esprima, e.g.
[babe-eslint](https://github.com/babel/babel-eslint).

But this packag requires Babel7.

```
"dependencies": {
"@babel/code-frame": "7.0.0-beta.36",
"@babel/traverse": "7.0.0-beta.36",
"@babel/types": "7.0.0-beta.36",
"babylon": "7.0.0-beta.36",
"eslint-scope": "~3.7.1",
"eslint-visitor-keys": "^1.0.0"
},
```

So should we update eventually? @onsetsu ?

Start by locating the ESLint parser integration and the package dependency configuration, then reproduce the parsing error with `foo::bar()`. Review the Babel 7-compatible parser option mentioned in the issue; done means the project syntax is accepted without an Esprima parsing error and the required dependencies are consistent.

Written by the indexing model from the issue text.