Fix incorrect image copies [#408] (#411)

* Fix copying every images that looks like <img> tag

Instead of doing regex search on markdown source,
(both markdown `![alt](/img/src/path "title")]` and html `<img src="/path" />`)
convert it to html first and then search only for html.

This fixes the problem of falsely trying to copy img tags that are not
actual images, but codes:

```html
<img src="please/dont/bother/copying" />
```

which is HTML-escaped and is safe from being caught by `htmlImageRe`.

* Fix image copy failure from throwing errors during static

It should just warn and continue.

lib/static.js

@@ -3,15 +3,14 @@ const fs = require('fs-extra');
 const path = require('path');
 const _ = require('lodash');
 const { getOptions, getAssetsDir, getPath, getStaticDir, getSlideOptions, getFilesGlob } = require('./config');
-const { isDirectory, isFile, parseYamlFrontMatter, getFilePaths, isAbsoluteURL } = require('./util');
+const { md, isDirectory, isFile, parseYamlFrontMatter, getFilePaths, isAbsoluteURL } = require('./util');
 const { revealBasePath, highlightThemePath } = require('./constants');
 const { renderFile } = require('./render');
 const { renderListFile } = require('./listing');
 const featuredSlide = require('./featured-slide');
 
 const files = new Set();
 
-const mdImageRE = /!\[[^\]]*\]\((.*?)\s*(["'](?:.*[^"'])["'])?\s*\)/g;
 const htmlImageRE = /<img.+src=["'](.+?)["'](?:.+?)>/g;
 
 const relativeDir = (from, to) => path.relative(from, to).replace(/^\.\./, '.');
@@ -63,13 +62,14 @@ const copyAssetsAndWriteFile = async (sourceDir, file, targetDir) => {
   const awaits = await copyAssetsFromOptions(markdown);
   const base = relativeDir(file, '.');
   const markup = await renderFile(path.join(sourceDir, file), { base });
-  let image;
 
-  while ((image = mdImageRE.exec(markdown) || htmlImageRE.exec(markdown))) {
+  let image;
+  const html = md.marked(markdown.toString());
+  while (image = htmlImageRE.exec(html)) {
     const [, imgPath] = image;
     if (!isAbsoluteURL(imgPath)) {
       const relPath = path.join(path.dirname(file), imgPath);
-      awaits.push(cp(path.join(sourceDir, relPath), path.join(targetDir, relPath)));
+      awaits.push(cp(path.join(sourceDir, relPath), path.join(targetDir, relPath)).catch((err) => console.warn(err)));
     }
   }