Added a couple of todolist items.

	modified:   TODO.md
created an instalation script

	new file:   install.sh
speedup: Don't redraw the blank-line markers if they haven't changed.

	modified:   editor.rb
speedup: don't update statusline more than 10 times per second

One issue left: if text is entered fast enough (pasted), then status
line may be wrong until next keypress event.

	modified:   editor.rb
bugfix: redraw blank lines if refesh=true

We need to clear the screen if the terminal size has changed.

	modified:   editor.rb
bugfix: return instead of next

Had copied code from a loop, but didn't change 'next' to 'return';

	modified:   editor.rb
bugfix: script to run editor.rb needs to have $@ at then end.

	modified:   install.sh