Key_event changes

Hey Team,

Uh after working on edit_box I noticed that our key_event structure is
stupid.  The keycodes represent just ascii not keys.  keys with ascii
counterparts should like up with ascii codes, but the keycodes.h should
represent the keys themselves (ie key_2 and key_at are not separate
keys).  We don't have a modifier list in our key_event either.  Would
anyone mind horribly if I totally revamped the key_event?

(So basic editting is now supported in the edit box, providing the
backend sends the appropriate keycodes - SDL does atm)

I think I might just copy the SDL structure and keycode list, adjusting
where necessary to be in the spirit of OO C++.

Darren