HTML-to-plaintext fails for <pre> text

[adam-p]

Reproduction

1. Go here or to any "raw" source page for a Github README (like ours).
2. Select-all, copy.
3. Paste into Gmail.
4. Click "Markdown Toggle".

Result: Pretty disastrous rendering. Specifically, it mostly looks like the whole text is being treated as a single line.

Preliminary diagnosis

jsHtmlToText (the library we use for HTML-to-plaintext) adds newlines to text based on tags, and doesn't pay attention to stuff like white-space: pre; -- which changes how newlines should be treated.

Possible solutions

• Make the HTML-to-plaintext processing more intelligent. E.g., check styles like white-space.
• Make the HTML-to-plaintext processing simple: just use innerText (or textContent in Gecko). It'll require proper testing, but some initial fooling around suggests it works well.

Workaround

Don't paste <pre> text. Paste plaintext or convert to plaintext (like with Gmail's "Strip formatting" button).

[adam-p]

This issue was forked from #9