Add support for RW2 and RAF file types

[mceachen]

If you're adding support for a new file type, please follow the below steps:

• One PR per file type (sorry, they're right next to each other).
• Add a fixture file named fixture.<extension> to the fixture directory.
• Add the file extension to the types array in test.js.
• Add the file type detection logic to the index.js file.
• Add the file extension to the FileType type in index.d.ts.
• Add the file extension to the Supported file types section in the readme, in the format - [`<extension>`](URL) - Format name, for example, - [`png`](https://en.wikipedia.org/wiki/Portable_Network_Graphics) - Portable Network Graphics
• Add the file extension to the keywords array in the package.json file.
• Run $ npm test to ensure the tests pass.
• Open a pull request with a title like Add support for Format, for example, Add support for PNG.
• The pull request description should include a link to the official page of the file format or some other source. Also include a link to where you found the file type detection / magic bytes and the MIME type.

Fixes #218

[przemyslawpluta]

@mceachen thanks @sindresorhus can you review and merge when you have a minute. Thanks.