"^**superbold**^" not parsing as expected

### The title says everything.
The `"^**superbold**^` should be display as superscript **and** bold,
but **only the superscript works**, the `**` remain unparsed ... :confused:
`**^superbold^**` **doesn't work** as well. `**lol^superbold^**` somehow **works perfectly**.

*The same behavior applies to`"^*supercursive*^`, ...*

Start by locating CodiMD's JavaScript Markdown parsing or rendering entry point and reproduce the reported superscript-plus-bold and superscript-plus-italic examples. Check the existing parsing behavior around the three examples in the issue; done means nested formatting renders as both superscript and bold or italic without regressing the case that already works.

Scritto dal modello di indicizzazione a partire dal testo della issue.