Allow users to edit the existing typed code in the editor about glorious-demo

[quinton-ashley]

It could look like this:

demo  
  .openApp('editor', {minHeight: '350px', windowTitle: 'demo.js'}) 
  .write(codeSegment0) //initial code 
  .write(codeSegment1, {insertAt:{line:2}}) // insert at start of line 2, default char 0
  .write(codeSegment2, {insertAt:{line:6, char:5}}) // insert after line 6, char 5
  .replace('', {from:{line:2}, to: {line:4}) // remove lines 2 through 4
  .replace(codeSegment3, {from:{line:8, char: 3}, to: {line:8, char: 10})
  .end()