Add support for new code element and attributes

[hubgit]

Support the use of <code> instead of <preformat> for code blocks.

http://www.mulberrytech.com/JATS/JATS-changes-for-1-1.pdf

http://jatspan.org/niso/publishing-1.1/#p=pe-code-atts

• @code-type (type of any non-programming example:
  XML tagged document, DTD, XSD)
• @code-version (version of the program or code fragment)
• @executable (yes or no)
• @language (programming or scripting language in which code is written, e.g., “javascript”)
• @language-version (version of the programming language, e.g. “3.0” for “Javascript 3.0”)
• @platforms (hardware and/or software platform(s) on which the code runs)