Interactive shell helpers

Some packages provide the shell integration to be more useful. But unlike other systems, nix doesn't have a standard share directory location. This is why a bunch PACKAGE-share scripts are shipped that print the location of the corresponding shared folder. Current list of such packages is as following:

• fzf : fzf-share

E.g. fzf can then be used in the .bashrc like this:

source "$(fzf-share)/completion.bash"
source "$(fzf-share)/key-bindings.bash"