Add cabal_sandbox_info function

Reports whether the current working directory is within a
sandbox. Useful to check before installing Cabal packages into the
global registry.
Fix URL to gi (gitignore) function

Previous URL doesn't seem to work because the host requires a www
prefix.
Merge pull request #2542 from puffnfresh/gitignore-plugin-url

Fix URL to gi (gitignore) function
Update gitignore.plugin.zsh

Fix URL to gi (gitignore) function in _gitignireio_get_command_list function
Fix remaining broken URL in gitignore function
Merge pull request #2541 from puffnfresh/cabal-sandboxes-info

Add cabal_sandbox_info function
Adieu l'ami.

 @jimweirich -- You will be missed.
Merge pull request #2544 from fduch2k/patch-1

Update gitignore.plugin.zsh
Merge pull request #2548 from puffnfresh/gitignore-plugin-url

Fix remaining broken URL in gitignore function