Support additional Encodings

[Jericho]

As discussed in #250 , StrongGrid fails when attempting to parse inbound emails if the content has been encoded with a charset that .netcore does not support by default.

One such encoding is Windows-1252 which is used by Hotmail's web interface when sending an email containing characters such as " ' " ' " ' " ! @ # $ % ^ & * ( ) - + = [ ] { } : ; ‘ ‘ “ “ ” ` ~. This encoding (and presumably other encodings as well) are not supported by .netcore by default and must be explicitly enabled.

StrongGrid should strive to support as many encodings as possible.