Fix glitch when rendering scrollbar on the right edge of the screen.

The old code was painting a white bar leading up to the scrollbar handle on my system.
Support prepped spell and held item indicators.

To use these, add this to your layout:

	<window class='indicator' top='lines-28' left='0' height='1' width='11' value='right' fg='444444,ffffff'/>
	<window class='indicator' top='lines-27' left='0' height='1' width='11' value='left' fg='444444,ffffff'/>
	<window class='indicator' top='lines-25' left='0' height='1' width='11' value='spell' fg='444444,ffffff'/>

and shrink your death/logons window by five lines to make space.

Ideally, lich should also send this information when profanity connects:

	init_str.concat "<right>#{GameObj.right_hand.name}</right>"
	init_str.concat "<left>#{GameObj.left_hand.name}</left>"
	init_str.concat "<spell>#{XMLData.prepared_spell}</spell>"
Interpret ^? as backspace.

This fixes backspace e.g. on the Mac without reconfiguring Terminal.
Add scroll_current_window_bottom key action.
Add basic readline-style kill and yank (cut and paste) support.

Example key bindings:

	<key id='ctrl+u' action='cursor_kill_line'/>
	<key id='ctrl+k' action='cursor_kill_forward'/>
	<key id='ctrl+y' action='cursor_yank'/>