refactor: Use haumea for filesystem-based module system for flake outputs

refactor: Use hyphen(`-`) for variable names & folder names(except Python), replace all unserscore(`_`) with hyphen(`-`).

hosts/darwin-harmonica/default.nix

@@ -0,0 +1,13 @@
+_:
+#############################################################
+#
+#  Harmonica - MacBook Pro 2020 13-inch i5 16G, mainly for personal use
+#
+#############################################################
+let
+  hostname = "harmonica";
+in {
+  networking.hostName = hostname;
+  networking.computerName = hostname;
+  system.defaults.smb.NetBIOSName = hostname;
+}