refactor: tidy structure of source files

Fixes #79

src/protocol/search/sorts/distance.ts

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2019 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+// tslint:disable-next-line:no-implicit-dependencies
+import {Position} from 'geojson';
+import {SCSearchAbstractSort, SCSearchAbstractSortArguments} from '../sort';
+
+/**
+ * Sort instruction to sort by distance
+ */
+export interface SCDistanceSort extends SCSearchAbstractSort<SCDistanceSortArguments> {
+  /**
+   * @see SCSearchAbstractSort.type
+   */
+  type: 'distance';
+}
+
+/**
+ * Additional arguments for sort instruction to sort by distance
+ */
+export interface SCDistanceSortArguments extends SCSearchAbstractSortArguments {
+  /**
+   * Position to calculate distances to
+   */
+  position: Position;
+}