The lambda that acts as the sentinel for building SBCL with packages
needs to be able to capture variables if lexical binding is enabled,
which is made possible by the lexical-let form.
Adds a function that can launch Sly with a pre-configured SBCL for a
Lisp derivation in the depot.
This makes it convenient to spin up development environments for Lisp
libraries and programs by simply calling `M-x nix/sly-from-depot RET
tools.something`.
This relies on `nix-depot-path` being configured currently as I have
not yet reliably added the depot to my NIX_PATH on all machines.
Adds an Emacs library with so far a grand total of one helper function
that can prefetch and insert a git repository at point.
This is very useful for the various Go repo imports I am doing at the
moment.
