Default encoding

[crawler]

Add the ability to set the default encoding for the responses that do not contain charset directive.

Faraday::Encoding.default_encoding = Encoding::UTF_8

[ma2gedev]

@crawler Thank you for your pull request!

I'm not sure why do we support this feature. Please provide me more information.

The faraday-encoding gem assumes the situation when a server provides content-type header with charset. So i think that this gem would not like to affect any modification to the response if there is no charset header.