Reader should only process lines in AsciiDoc files

additionally:

- small optimization for matching line comments
- decrement look_ahead if line restored w/ processing off
fix false detection of list item with hyphen marker
Merge pull request #585 from mojavelinux/preprocess-asciidoc-only

Reader should only process lines in AsciiDoc files
Merge pull request #586 from mojavelinux/fix-invalid-list-match

fix false detection of list item with hyphen marker