Support nested bold and italic text in code listings that use syntax highlighting.

Currently if you mark something up as:
<emphasis role="bold"><replaceable>yourAuthToken</replaceable></emphasis>
the regular expressions that obfuscate the html in the code listing to protect it
from the syntax highlighting become confused because they use the same
string to hide the markup. This fix uses a different sequence for bold (;;;;) and html (!!!!).

Change-Id: I9a1e6304ffbe3f9a9dc75a8d5074c9fd481a0c4e