Implement --prompt-bottom and --result-bottom-up options (same as percol)

normal:
![peco__ls_-g_-l_____peco__peco__tmux](https://cloud.githubusercontent.com/assets/58161/3511716/40ddf764-06b2-11e4-8f06-7161963dd48f.gif)

`--prompt-bottom`:
![peco__ls_-g_-l_____peco_--prompt-bottom__comparing_master___reverse-result-mode__keqh_peco](https://cloud.githubusercontent.com/assets/58161/3511725/5511b748-06b2-11e4-93e8-727a85abc8b3.gif)

`--result-bottom-up`:
![peco__ls_-g_-l_____peco_--result-bottom-up__comparing_master___reverse-result-mode__keqh_peco](https://cloud.githubusercontent.com/assets/58161/3511732/65b9dada-06b2-11e4-8246-c43fd16a21a7.gif)

`--prompt-bottom` and `--result-bottom-up`:
![peco__ls_-g_-l_____peco_--result-bottom-up_--prompt-bottom__peco__tmux](https://cloud.githubusercontent.com/assets/58161/3511746/79cee31c-06b2-11e4-8216-b2b54cda6f3a.gif)

refs: [Prompt at the bottom · Issue #9 · mooz/percol](https://github.com/mooz/percol/issues/9)