Refactoring for heading processing for PDF bookmarks.
Merge branch 'master' of github.com:oreillymedia/HTMLBook into pdf-bookmarks
Moving "process-headings" template to common.xsl
"process-heading" tests.
"process-heading" tests for table and figure captions.
use "process-heading" template mode for generating PDF bookmark attrs.
Refactoring heading processing code, to eliminate duplicate code and make reuse for PDF bookmark attr possible.
Preserve data-pdf-bookmark on elements, if it already exists.
new param for toggling labels in PDF bookmarks.
Merge pull request #102 from oreillymedia/pdf-bookmarks

Refactored heading handling and added parameterized support for labels in PDF bookmarks