style: normalize formatting

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Overview:

  - normalize function formatting:
      - function statement: `function f() {}`
      - function expression: `function() {}`

  - `disallowQuotedKeysInObjects: true` (e.g. `{foo: 42}` rather than `{'foo': 42}`)

  - `requireSpaceAfterLineComment: true` (e.g. `// comment` rather than `//comment`)

  - `validateIndentation: 4`

I prefer two spaces for indentation, and this style is currently used in some of the project's files, but __ramda.js__ itself uses four spaces so I went with that. If you'd like to switch to two spaces I'll update this pull request. :)

How is __ramda.api.js__ used?

i'm fine with that style for `if/else` blocks. 

this reminds me that there is a bug in `else if (R.is(String, set1)) { return set1.concat(set2); }`; should be `else if (R.is(String, set1) && R.is(String, set2)) { return set1.concat(set2); }`;