New issue with mailto links

Links containing an embedded '@' should not create an email link.
minor syntax changes, alias header? to has_header? on Document
resolves #863 allow doctype to be set in AsciiDoc table cell
Set background color on toc2 to cover scrolling content
Merge pull request #860 from @neher
Merge pull request #864 from mojavelinux/issue-863

resolves #863 allow doctype to be set in AsciiDoc table cell
resolves #866 don't match e-mail address inside URL
Merge pull request #849 from @LightGuard
optimize several loops (remove use of inject)
interpolation is faster than dup for string
use nowrap option of Pygments to simplify post-processing
minor syntax cleanups
minor syntax cleanups
more efficient way to check for Extensions class
optimizations and syntax cleanups
remove ERB from HTML5 document template
minor cleanups
minor optimization
remove ERB from most DocBook templates; add some missing DocBook tests
remove remaining uses of ERB internally