resolves #495 add attribute to keep lines that have an undefined attribute

- add tests for dropping (or not dropping) lines with an undefined attribute
change assert_not_match to assert_no_match to make Ruby 1.8 happy
Merge pull request #497 from mojavelinux/ignore-undefined

resolves #495 add attribute to keep lines that have an undefined attribute
resolves #498 permit !name syntax for undefining attribute

- remove unused attribute matching regular expressions
- normalize negated attributes before processing other assignments
- improved attribute tests
Merge pull request #499 from mojavelinux/bang-before-attribute-name

resolves #498 permit !name syntax for undefining attribute
rbx is broken again, cannot find ERB, disable until installation is fixed
resolves #504 sanitize contents of HTML title element in html5 backend

- also use 'Untitled' for HTML title when doctitle is nil
localize "Untitled" string