Fix keys

This PR tries to normalize the inconsistencies between exiftool and exifreader. Turns camel-case into lower case words. Basically:

`ISORate` => `iso rate`
`YResolution` => `y resolution`
`PixelYDimension` => `pixel y dimension`

Also uses the description instead of the funky `PixelYDimension: { value: 100, description: 100 }`.

also, @visionmedia could you give me access to NPM publishing for this repo?