Reduce overhead of specifying new links in Makefile

[GuiltyDolphin]

Currently, specifying new links in the Makefile takes
the following form (for example):

.PHONY: link_ghci
link_ghci : install_ghci # currently requiring the program be installed before linking
	$(call linkf,haskell/.ghci,.ghci)

It would be nice to just be able to specify links in the
format of a map:

links = {
  'haskell/.ghci'   => '.ghci',
  'dotdir/.../file' => 'path/from/home',
}

For example.