EPUB foundations

This pull requests includes:
 * Stability enhancements to LaTeXML::Converter, namely: 
    * Improved error reporting infrastructure, better eval encapsulation of the option sanity check.
    * Code refactoring of the intermediate exit routes from the Converter::convert processing, triggered by Fatal errors.

 * Better "whatsout" handling infrastructure - now in a separate Post::Pack post-processor
 * Math "whatsin" is now handled properly via the two special \ensuremathfollows and \ensuremathpreceeds macros, invoked via a wrapping preamble-postamble pair.

 * New option defaults, implicit behavior and sanity checks for various archive-based output formats (EPUB, Mobi) as well as the generic ZIP target.

 * New abstract Manifest post-processor, concrete EPUB manifest processors to follow.

 * Changes in indentation at a number of locations. Could be considered spurious and should ideally be processed with perltidy as soon as possible.


Please review the code differences bellow and suggest enhancements that would make a merge acceptable. I apologize for not making the pull request smaller and with finer granularity, but that is due to porting existing code from the SVN repository. I hope with newer git-based commits that follow up on this pull request, the merge suggestions will be much more manageable.