Enable creation of other config files than init.lua (#246)

wrappers/modules/files.nix

@@ -0,0 +1,64 @@
+modules: {
+  pkgs,
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib) types;
+  fileModuleType = types.submodule ({
+    name,
+    config,
+    ...
+  }: {
+    imports = modules;
+    options.plugin = lib.mkOption {
+      type = types.package;
+      description = "A derivation with the content of the file in it";
+      readOnly = true;
+      internal = true;
+    };
+    config = {
+      path = name;
+      type = lib.mkDefault (
+        if lib.hasSuffix ".vim" name
+        then "vim"
+        else "lua"
+      );
+      plugin = pkgs.writeTextDir config.path config.content;
+    };
+  });
+in {
+  options = {
+    files = lib.mkOption {
+      type = types.attrsOf fileModuleType;
+      description = "Files to include in the vim config";
+      default = {};
+    };
+
+    filesPlugin = lib.mkOption {
+      type = types.package;
+      description = "A derivation with all the files inside";
+      internal = true;
+      readOnly = true;
+    };
+  };
+
+  config = let
+    files = config.files;
+    concatFilesOption = attr:
+      lib.flatten (lib.mapAttrsToList (_: file: builtins.getAttr attr file) files);
+  in {
+    # Each file can declare plugins/packages/warnings/assertions
+    extraPlugins = concatFilesOption "extraPlugins";
+    extraPackages = concatFilesOption "extraPackages";
+    warnings = concatFilesOption "warnings";
+    assertions = concatFilesOption "assertions";
+
+    # A directory with all the files in it
+    filesPlugin = pkgs.buildEnv {
+      name = "nixvim-config";
+      paths = lib.mapAttrsToList (_: file: file.plugin) files;
+      ignoreCollisions = true; # Collisions can't happen by construction
+    };
+  };
+}