add format_appendix to accept to switch appendix number style
Merge branch 'master' into appendixstyle
null check.
Add tests and refactoring
Fix prefix mistake
Merge branch 'master' into appendixstyle
Set config to chapter's book
Fix chapter's format_number in lavel2 case
Merge pull request #295 from kmuto/appendixstyle

add format_appendix to accept to switch appendix number style (fix #294)