avoid markdown <em> and <strong> in link title

<em> and <strong> is avoide in link href but not in link title. 

So url like http://foo.com/blah_blah_blah/123 would be:
<p><a href="http://foo.com/blah_blah_blah/123">http://foo.com/blah<em>blah</em>blah/123</a></p>

I think link title must be avoid markdown <em> and <strong>.