Unix config normalization

[noraj]

It's really nice to have Configuration files with ffufrc.
However having ~2000 "dotfiles" in $HOME is a bit less nice.

That why I suggest implementing a XDG compliant config deployment.

• Specs: XDG Base Directory Specification
• Env vars: XDG_CONFIG_HOME (default to $HOME/.config for users) and XDG_CONFIG_DIRS (default to /etc/xdg for system)
• Go libs: go-appdir (archived) - configdir (abandoned) - kyoh86/xdg (archived) - adrg/xdg (up to date)

The idea would be to have ~/.config/ffuf/config.ini instead of the legacy ~/.ffufrc.

[daniel-ts]

My pull request addresses this issue. See #582.

Basically, ffuf would look for .ffufrc first in the current working directory, then in $XDG_CONFIG_HOME/.ffufrc on Linux and then $HOME/.ffufrc.

This pull also provides a mechanism to merge configuration from different sources sanely. The default hierarchy would be .ffufrc < request file < explicit config file < commandline args.

[noraj]

I guess this issue has been covered by 2.0 release. #582 still introduces more changes and simplifications.