Feature Request: Split into two functions: getMimeType() + validateMimeType()

[k-funk]

I'd like to use this same lib not only for validation, but determining which type a given file is as well.

Signatures

function getMimeType(file?: File): { baseType, type } {
  ...
}

function validateMimeType(file?: File, acceptedFiles?: string | string[]): boolean {
  ...
  const { baseType, type } = getMimeType(file)
  ...
}

Sample Usage

const myFile = <a file>

if (!validateMimeType(myFile)) { throw new Error('not a valid file type') }

if (getMimeType(myFile).baseType === 'image') {
  // present preview of the image
} else {
  // present a generic file icon
}

[rolandjitsu]

@k-funk PRs are welcomed, so go ahead.