add putInfo method

lib/mbtiles.js

@@ -602,3 +602,22 @@ MBTiles.prototype.putGrid = function(z, x, y, data, callback) {
     if (++this._pending < 100) return this._commit(callback);
     else return callback(null);
 };
+
+MBTiles.prototype.putInfo = function(data, callback) {
+    if (typeof callback !== 'function') throw new Error('Callback needed');
+    if (!this.open) return callback(new Error('MBTiles not yet loaded'));
+    if (!this._isWritable) return callback(new Error('MBTiles not in write mode'));
+
+    // Valid keys.
+    var keys = [ 'name', 'type', 'description', 'version', 'formatter',
+        'bounds', 'center', 'minzoom', 'maxzoom' ];
+    for (var key in data) {
+        if (keys.indexOf(key) < 0) return callback("Can't set key " + key);
+    }
+    var stmt = this._db.prepare('REPLACE INTO metadata (name, value) VALUES (?, ?)');
+    stmt.on('error', callback);
+    for (var key in data) {
+        stmt.run(key, String(data[key]));
+    }
+    stmt.finalize(callback);
+};