Add more verbose error message

Add more verbose error for duplicate paths while generating TOC
Merge pull request #1 from jangxyz/patch-1

Add more verbose error message
Fix Korean ISBN rendering
Add link to Help page
Implement page revision (no diff yet)
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Add more HTML5 validation tests
Tweak HTML/CSS

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Tweak table CSS
Update JS libraries
Improve "search by link"
Tweak HTML/CSS
Fix null date formatting
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Tweak HTML/CSS
.config에 default_permissions 값이 없으면 KeyError 발생
Merge pull request #2 from jaewoo/master

.config에 default_permissions 값이 없으면 KeyError 발생
Remove duplication in get_default_permissions()
Optimize WikiPage._similar_titles
Optimize permission checking