Detect math blocks that are children of list items

[bertin0]

If I have a math block that is indented so that it is a child of a list item, pandoc treats it accordingly, but vim-pandoc doesn't recognize that it's a math block and so it doesn't enable syntax highlighting:
For example, this math block doesn't get highlighted, but pandoc treats it as latex:

1.  Test

    $$
        f(x) &=x\\
    $$

Just realised this is an issue in vim-pandoc-syntax, sorry

[user202729]

Note that this issue only happen if

• The formula is indented by at least 4 spaces, and
• It's at the start of the line. (so this doesn't cause the error)

1.  Test

    a $$
        f(x) &=x\\
    $$

As a workaround it's possible to disable detection of simple code blocks #221 (however simple code blocks will no longer works)

[user202729]

Duplicate of #139