Indentation is removed from triple-backtick code blocks

[oantolin]

There are two ways to write code blocks in StackExchnge sites:

• Original Markdown syntax: indent each line by four spaces
• GitHub-Flavored Markdown syntax: put the code block within triple-backquotes.

The 4-space indented blocks display correctly in sx.el, but the triple-backquoted ones lose their whitespace and get crammed into just a few lines. This question has two answers each using a different syntax for the block and you can see the difference if you visit it in sx.el: question with two types of code block.