feature: Desired column

When using up/down arrows, remember the column we were on.

	modified:   filebuffer.rb
cleanup: merged delete and backspace into same method

	modified:   filebuffer.rb
	modified:   keymap.rb
	modified:   editor.rb
cleanup: removed some duplicate code in indentation facade.

	modified:   filebuffer.rb
cleanup: merged duplicate code in undo/redo

	modified:   filebuffer.rb
cleanup: significantly simplified syntax coloring

	modified:   editor.rb
	modified:   syntaxcolors.rb
cleanup: minor duplication reduction in screen up/down stuff

	modified:   bufferslist.rb
	modified:   filebuffer.rb