revert to upstream
merge with bgwin branch

Squashed commit of the following:

commit 9b56c4e84107f9476b6fdf4103f6fdcb13949090
Author: Eon S. Jeon <esjeon@hyunmu.am>
Date:   Tue Sep 30 22:09:09 2014 +0900

    bind mod-minus to togglebg

commit 0f0ff9f84d94b1150f8ca3cd42af65cfb388a211
Author: Eon S. Jeon <esjeon@hyunmu.am>
Date:   Tue Sep 30 22:08:26 2014 +0900

    code formatting

commit 79f27e17d0400841db0b394fe19b765af74f4d0f
Author: Eon S. Jeon <esjeon@hyunmu.am>
Date:   Tue Sep 30 22:07:41 2014 +0900

    remove TODOs

commit 1a400e75da9c784e0b28a1774bd078a915056c05
Author: Eon S. Jeon <esjeon@hyunmu.am>
Date:   Tue Sep 30 20:23:08 2014 +0900

    initial implementation

commit 3b52f14c9e52461280258a94533c5748ed02c57a
Author: Eon S. Jeon <esjeon@hyunmu.am>
Date:   Tue Sep 30 19:11:07 2014 +0900

    working on...