Feature Request: multiple highlight colors

[Thylane]

Description: Support multiple highlight colors.
For example, the code block below specify the 2nd row is highlighted in red, the 3rd in green, the 4th in blue.

```java TI:"Hello World" HL:"R[2], G[3], B[4]"

It's userful when I want to highlight the change of code, like what github does.

[Thylane]

Actually I have changed the code to make this work for me, now the rendered code block looks like this:

Here's the detail:

Check the DOM

<!-- In my case the line height is 1.5em -->
<div class="code-block-highlight-wrap color-r">     <!-- red color  -->
  <span style="margin-top: 1.5em;"></span>          <!-- highlight the 2nd line -->
</div>
<div class="code-block-highlight-wrap color-g">     <!-- green color -->
  <span style="margin-top: 3em;"></span>            <!-- highlight the 3rd line -->
</div>
<div class="code-block-highlight-wrap color-b">     <!-- blue color -->
  <span style="margin-top: 4.5em;"></span>          <!-- highlight the 4th line -->
</div>

Modification to AnalyseHighLightLines

function analyseHighLightLines(str) {
  str = str.replace(/\s*/g, "");
  let hlLines = {};
  let matches = [...str.matchAll(/(R|G|B)\[(.*?)\]/g)];   // Get colors and corresponding lines.
  matches.forEach(match => {
    hlLines[match[1]] = (hlLines[match[1]] || []).concat(doAnalyse(match[2]));
    // doAnalyse does the same thing as the original function (analyseHighLightLines)
  });
  return hlLines;
  // Note that now it's not compatible with the old highlight syntax.
}

Modification to AddLineHighLight

function addLineHighLight(plugin, preElm, cbMeta) {
  let colors = Object.keys(cbMeta.highLightLines);
  let lineHeight = 1.5;   // assume it's 1.5em

  colors.forEach(color => {
    let highLightWrap = document.createElement("div");
    highLightWrap.className = "code-block-highlight-wrap color-" + color.toLowerCase();

    let indice = cbMeta.highLightLines[color].sort((a,b) => a-b);   // to make margin-top work properly
    let lastI = 0;
    for (let i of indice) {
      let singleLine = document.createElement("span");
      singleLine.style.marginTop = ((i - lastI - 1) * lineHeight) + "em";   // position the highlight element to the specified line
      lastI = i;
      highLightWrap.appendChild(singleLine);
    }
    preElm.appendChild(highLightWrap);
  });
  // Note that I ignore the plugin setting and I set the colors in css (not present here).
}