Minor cleanup coding format of <code>...</code>

[haxpor]

<code>...</code> is still there. I'm not sure this tag should be automatically handled by asciidoctor, if so it should be some option to fully clean it up I guess.

At any rate, it would be great to clean this tag up.

PS. I'm using release tag 2018.03.11 if using latest commit, generated man page files' filename *.3 will also include template argument like std::something<Arg1,Arg2>:: .... (that is for another issue).