Update Tetengo2
Change template parameters of tetengo2::gui::widget::traits::widget_traits and abstract_window_traits (wip) kaorut/tetengo2#18
Won't compile.
Revert "Change template parameters of tetengo2::gui::widget::traits::widget_traits and abstract_window_traits (wip) kaorut/tetengo2#18"

This reverts commit 983959284055c5549de1ff13da1f9afba4cd98c8.
Change template parameters of tetengo2::gui::drawing::picture_reader kaorut/tetengo2#18
Change template parameters of tetengo2::gui::drawing::solid_background kaorut/tetengo2#18
Update Tetengo2
Merge branch 'tparam'