The current wrapper only includes vim, gvim and the man pages
(optionally). This rewrite distinguishes two scenarios, which I expect
cover the majority of use cases:
- standalone mode, when `name != "vim"`, means the user already has a
vim in scope and only wants to add a customized version with a
different name. In this case we only include wrappers for `/bin/*vim`.
- non-standalone mode, when `name == "vim"`, means the user expects a
normal vim package that uses the specified configuration. In this case
we include everything in the original derivation, with wrappers for
all the executables that accept a vimrc.
update.py and its companion update-shell.nix need to know where they are, else
they can't find the root default.nix of Nixpkgs. Because of this, I further
added a small piece of documentation about those path-dependent pieces of code.
