Major release with hooks instead of pre-configured options

Breaking changes in 3.0.0 from 2.1.0:

• Removed simpleclip support, use a custom hook instead:
  https://github.com/etu/webpaste.el#copy-url-to-the-clipboard
• Removed sprunge.us as provider in
  5c742bf due to hosting issues for
  the foreseeable future.

New features in 3.0.0 from 2.1.0:

• Add support to parse language of file from shebang
• Add flag to totally ignore language for all providers. This flag is
  named webpaste-paste-raw-text and if set to t webpaste won't do
  any language detection. This is available as a customizable variable.

Provider news in 3.0.0 from 2.1.0:

• Add nix language to some providers
• Add toml language to some providers

Project news in 3.0.0 from 2.1.0:

• Add direnv files for nix-shell for easier development of the
  library if on NixOS.
• Add Emacs 26.1 to the tests.
• We had 25 commits by a total of 2 authors since 2.1.0 that was
  released on 27th of January 2018 (about 339 days ago).