Add temporary option "--future-format"

...for new experimental shell function handler.
Highlight executable files green
cbreak() --> raw() to get more keys
Require Escape/Alt for printable chars

This is needed for the filter, so we can just type without entering some
mode.
Pressing printable keys add these to the filter

Update the statusbar with current filter string.
Added filter functionality

Statusbar shows current filter string. Entry will be filtered out if neither
the identifier nor the path contains the entered string.

Other things that changed:
- KeyHandlerFunction: return bool to indicate if the handler was successfull
  Having this, we can press CTRL-C/CTRL-D to kill the filter, and then this again
  to quit
- Properly chop lines when printing (otherwise they will be wrapped to the next
  line)
- Use werase() instaed of wclear(), which flickers for urxvt
- Do nothing when user hits RETURN on empty or non existent items