Make virtual dom widget for code coverage display

Based on istanbul reporter

``` html

Code coverage report for examples/calc.js

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17 

1×

1×

 

 

1×

 

 

 

1×

 

 

 

 

 

1×

 
// example program to be instrumented

function add(a, b) {

  return a + b

}

 

function sub(a, b) {

  return a - b

}

 

function abs(x) {

  if (x < 0) {

    return -x

  }

  return x

}

console.log('2 + 3 =', add(2, 3))

 

```

Start by reviewing the issue's Istanbul reporter reference and the embedded HTML coverage report example. Identify the project's existing virtual DOM entry points, if any, before deciding how the widget fits in. Done should mean a virtual DOM widget can render the shown code coverage information, including line counts, coverage markers, source text, and the covered or uncovered styling.

Written by the indexing model from the issue text.