Support sqlite mode flags (#73)

* Update mbtiles.js

* some reading

* remove seemingly unused/dead code

* core api functionality

* test note

* grids

* remove index test

* add tilelive example

* vNext

* follow sqlite3 URI filenames

* add mode test

* add mode test

* fix ci

* fix ci

* Update mbtiles.js

* follow sqlite3 URI filenames

* add mode test

* add mode test

* fix ci

* fix ci

* Update readme on mode flags

test/mode.test.js

@@ -0,0 +1,32 @@
+require('sqlite3').verbose();
+
+var fs = require('fs');
+var MBTiles = require('..');
+var tape = require('tape');
+
+var non_existent = __dirname + '/fixtures/non_existent.mbtiles';
+
+try { fs.unlinkSync(non_existent); } catch (err) {}
+
+tape('Open with ro mode', function(assert) {
+  new MBTiles(non_existent + '?mode=ro', function(err, mbtiles) {
+    assert.ok(err);
+    assert.ok(err.message.match(/SQLITE_CANTOPEN: unable to open database file/));
+    assert.end();
+  })
+})
+
+tape('Open with rw mode', function(assert) {
+  new MBTiles(non_existent + '?mode=rw', function(err, mbtiles) {
+    assert.ok(err);
+    assert.ok(err.message.match(/SQLITE_CANTOPEN: unable to open database file/));
+    assert.end();
+  })
+})
+
+tape('Open with rwc mode', function(assert) {
+  new MBTiles(non_existent + '?mode=rwc', function(err, mbtiles) {
+    assert.notOk(err);
+    assert.end();
+  })
+})