Improve accepts definition, update raw-body

[blakeembrey]

Please fill in this template.

• Make your PR against the master branch.
• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run tsc without errors.
• Run npm run lint package-name if a tslint.json is present.

If changing an existing definition:

• Provide a URL to documentation or source code which provides context for the suggested changes: https://github.com/jshttp/accepts
• Increase the version number in the header if appropriate.
• If you are making substantial changes, consider adding a tslint.json containing { "extends": "../tslint.json" }.

[dt-bot]

accepts/index.d.ts

to author (@Bomret). Could you review this PR?
👍 or 👎?

Checklist

• pass the Travis CI test?

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raw-body/index.d.ts

to author (@Bomret). Could you review this PR?
👍 or 👎?

Checklist

• pass the Travis CI test?

[Bomret]

Very nice, thanks 👍