Purge out constants from classes, lowercase TERM_24_BIT

Remove recursive import as well
Add support for italic and underline attributes in shell renderer
Add a way to specify renderer options on command-line, added tmux_escape

Note: tmux escaping does not fix things, on my system it produces
![Gap between ... and directory name](http://img-fotki.yandex.ru/get/6439/9151298.2/0_93b4c_5d9a317f_orig.png)
Fixes #199
Add screen_escape option

Refs #199.