Apparently it is possible for the config to be compiled correctly but
for ‘hint’ still not know where the packages are: it seems to ignore the
GHC in PATH and does whatever.
Now to use Yi along with its config the user passes all the extra
libraries wanted by their config as extraPackages and builds the
expression. This means there is no hassle from the user about having to
manually create a cabal file and wrap over the Yi binary.
