feat(nix/buildLisp): Add initial sketch including buildLisp.library

Adds a Nix function to build a Lisp library out of a specified set of
Nix files. All files are combined into a single FASL.

This is by design only compatible with SBCL (for now).

nix/buildLisp/README.md

@@ -0,0 +1,21 @@
+buildLisp.nix
+=============
+
+This is a build system for Common Lisp, written in Nix.
+
+The project is in its early stages and currently supports nothing
+other than compiling a bunch of Lisp sources into a combined FASL
+file.
+
+This is what it currently looks like:
+
+```nix
+nix.buildLisp.library {
+  name = "test-lib";
+  srcs = [
+    ./nix/buildLisp/test-lib.lisp
+  ];
+}
+```
+
+Check back here in a few days for more information.