Nonempty sequence of inline elements can be the contents of an strongly emphasized span

[sawyerh]

Creating a link inside of a bold string gets messed up when you toggle between Markdown mode and WYSIWYM mode. It seems to only happen when the bold string ends with the link (the ending parentheses followed by a double asterisks).

Example:

Some **bold text wrapping [a link](/test)**

Changes to

Some **bold text wrapping [a link**](/test)

Which then changes to

\*\*Some bold text wrapping [a link\*\*](/test)

I don't believe this conforms to the CommonMark Spec (see Example 390)

Tested on http://prosemirror.net/demo/markdown.html in Chrome 49.

cc #19

[sawyerh]

Looks like this was fixed with #216, but isn't in the current release. Apologies for the false alarm.