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Adds "givero" as a keyword for searching Givero, a relative new search engine donating revenue to good causes around the world.

Changed from `stack` because it conflicts with Haskell Tool Stack

Fixes #7659

Co-authored-by: Maxime AURIAU <maxime.auriau@dnd.fr>

Substitutes the current duplicate logic for the standard
and cross-platform function open_command in plugins:

  frontend-search, jira, node, web-search

- if user has rm set as an alias to 'rm -i' user is prompted to whether to
  remove the nohup.out file.

 $ ddg fools
	nohup: ignoring input and appending output to ‘nohup.out’
	rm: remove regular empty file ‘nohup.out’?

- if output redirected to a file nohup will not create nohup.out and rm is
  unecessary.

The $OSTYPE variable is set at ZSH compile time and can be safely used
to determine the OS of the system. e.g. darwin (os x)

This plugin adds google, bing and yahoo commands to launch the default
web browser to do web search:

e.g.

    google oh-my-zsh
    bing what is zsh