Store encoding metadata

[josephmturner]

Currently, hypercore-fetch assumes that all text files are UTF-8 when returning a Content-Type header:

function getMimeType (path) {
  let mimeType = mime.getType(path) || 'text/plain; charset=utf-8'
  if (mimeType.startsWith('text/')) mimeType = `${mimeType}; charset=utf-8`
  return mimeType
}

In order to return the actual coding system for a file, we'd need to know how the file was encoded when it was written to the hyperdrive.

IIUC, the standard way to specify a file's encoding in a PUT request is in the Content-Type header, e.g., Content-Type: text/plain; charset=ISO-8859-1.

Once hypercore-fetch receives the file and its coding system, where should the encoding metadata be stored?

We could put it alongside the mtime metadata in entry.value.metadata.encoding. WDYT?