build: Converted Makefile and flake package.

cmd_version.odin

@@ -0,0 +1,12 @@
+package main
+
+import "core:fmt"
+
+cmd_version :: proc(cmd: ^Command) {
+	if has_flag(cmd, "long") || has_flag(cmd, "l") {
+		fmt.printf("envr version %s\n", VERSION)
+	} else {
+		fmt.println(VERSION)
+	}
+}
+