Use in-memory dbs for most of the test suite

The only thing left to do is to refactor z-webmention-test. I tried
but I got eaten by a grue.

Ref #31

test/lib/app.js

@@ -26,14 +26,15 @@
 
 var assert = require('perjury').assert,
     noopLog = require('./log'),
+    memoryPersistence = require('./persistence').memoryPersistence,
     _ = require('lodash');
 
 function configureAppSetup(config) {
 	return {
 		topic: function() {
 			var app = require('../../lib/app').makeApp(_.defaults(config, {
 				domains: []
-			}), noopLog, require('../../lib/persistence')('/tmp')),
+			}), noopLog, memoryPersistence()),
 			cb = this.callback;
 
 			var server = app.listen(config.port || 5320, config.address || 'localhost', function(err) {

test/lib/persistence.js

@@ -55,4 +55,22 @@ function wrapFsMocks(configurePath, obj) {
 	return _.assign({}, buildMockSetup(configurePath), obj);
 }
 
+function makeInMemoryPersistence() {
+	var store = new Map();
+
+	return function() {
+		return {
+			get: function(namespace, key, cb) {
+				process.nextTick(cb.bind(undefined, undefined, store.get(namespace + key) || {}));
+			},
+			set: function(namespace, key, data, cb) {
+				store.set(namespace + key, data);
+				process.nextTick(cb);
+
+			}
+		};
+	};
+}
+
 module.exports.wrapFsMocks = wrapFsMocks;
+module.exports.memoryPersistence = makeInMemoryPersistence;