v4.0.0 update

[xXBuilderBXx]

• Remove 3 shutdown booru sources.
• Add cookie header support for captcha or block based boorus.
• Set rule34 and Gelbooru to require auth.
• Set atf booru to require cookie.
• Rename booru options to booru flags.
• Add a new booru options class with client options to set such as auth, cookie and proxy.
• Add support for web proxy.
• Check for xml or json response responses.
• Fixed Danbooru source.

Breaking change if you use the old BooruOptions with new Aboouru(BooruOptions.Flag) this has been changed to new Abooru(new AbooruOptions { Flags = BooruFlag.Flag })

New BooruOptions settings which exposes:
Auth - previously set in Abooru now moved.
Flags - moved from new Abooru()
Cookie - Added to support captcha blocks.
Proxy - Used to set a proxy service for requests.