Improve verbose mode logging

- Support passing a log message function to `logging.log` for lazy
  evaluation
- Log results (or at least lengths) of all API functions
- Log merged config during initialisation
- Log distance calculation duration

src/main.js

@@ -1,6 +1,7 @@
 import Vue from "vue";
 import App from "@/App.vue";
 import config from "@/config";
+import { log } from "@/logging";
 import i18n from "@/i18n";
 import router from "@/router";
 import store from "@/store";
@@ -12,6 +13,8 @@ Vue.use(VOutsideEvents);
 
 Vue.config.productionTip = false;
 
+log("CONFIG", config);
+
 Vue.prototype.$config = config;
 
 new Vue({