joins the parsing of links and emphasis, fixing the precedence issues (see examples 520, 521, and 522)
simplifies link delimiter parsing -> one pass only, no recursive parsing
fixes the handling of consecutive and trailing spacing -> inline spacing is preserved (see 652), needed for nested emphasis content
removes the need for fallback with inline link destination and link attributes in general -> these are matched only once the link is successful (as example, this would previously not be parsed as emphasised link *[[]()](*))
This PR:
*[[]()](*)
)underscores
option to emphasis