closes #29
fixes #26

Squashed commit of the following:

commit b1f0dda5f7bff459c43659c5c9d22af09289f875
Author: Olivier Yiptong <olivier@olivieryiptong.com>
Date:   Thu Oct 30 16:48:21 2014 -0400

    comment on order_by usage

commit 63567a6fbad34e0e5e286636d319ee0204f6d600
Author: Olivier Yiptong <olivier@olivieryiptong.com>
Date:   Thu Oct 30 16:43:57 2014 -0400

    remove database lock from queries.insert_tile

commit 982416cee27c43ef8b662d3348750c7e0a6d2d5c
Author: Olivier Yiptong <olivier@olivieryiptong.com>
Date:   Thu Oct 30 16:37:17 2014 -0400

    lock tiles table for each tile insert

commit 7ad3487f0f84e5ceaebbe1f9575c4227b67cf2de
Author: Olivier Yiptong <olivier@olivieryiptong.com>
Date:   Thu Oct 30 16:36:48 2014 -0400

    in case of duplicate tiles, use the lowest id
version bump 1.0.11
merge with master