Feature Request: allow custom datetime parser

[mayoms]

It's not guaranteed that dates for incoming emails will be compliant with Mail.Parsers.RFC2822.to_datetime/1 implementation, which requires forking, patching or a PR to address. If the datetime parser was modular, and either passed in or set via configuration it would allow the end-user the flexibility to handle these cases in their application code. This would be something similar to the optional parser argument in Mail.parse, e.g.

defmodule CustomDateParser do
  def to_datetime(<<custom_string_match>> = date_str) do:
    # custom parser
  end

  # fallback to default implementation
  def to_datetime(date_str), do: Mail.Parsers.RFC2822.to_datetime(date_str)
end

Mail.parse(email, Mail.Parsers.RFC2822, CustomDateParser)

I'd be happy to contribute such a change if interested.

[andrewtimberlake]

Closing because of #169