Nested em and strong aren't highlighted. Horizontal lines mistakenly highlighted as italics

[rafi]

1. **Combined strong and _emphasize_** is htmlBold, but _emphasize_ should be htmlItalic
2. _Combined emphasize and **strong**_ is htmlItalic, but **strong** should be htmlBold
3. Horizontal lines with * or _ are highlighted wrongfully as htmlBoldItalic