Use the latest version of NekoHTML (1.9.20)

The use of self-closing 'a' tags causes a problem in the guides index
page. Self-closing 'a' tags are not legal HTML 5. The only tags which
may be self-closed are void tags. See [1] for more information.

With the upgrade to 1.9.20, the self-closing tag is treated as still
being open and a nested 'a' tag is then encountered. When this tag is
closed, it's actually the self-closing tag which is closed which
causes the stack to unwind prematurely. This causes expression
evaluation to fail (${guide} is null) as the expression context is
incorrect.

The page in question has been updated to replace <a/> with <a></a>.

[1] http://www.w3.org/TR/html5/syntax.html#void-elements
Merge pull request #395 from wilkinsona/nekohtml-1.9.20

Use the latest version of NekoHTML (1.9.20)
Make fields final where appropriate
Add class-level Javadoc
Replace PostViewFactory with static PostView methods
Optimize imports globally
Format sources globally
Reduce visibility where appropriate
Add class-level Javadoc for sagan.docs.support.*
Add class-level Javadoc for sagan.projects.support.*
Add class-level Javadoc for sagan.search.support.*
Add class-level Javadoc for sagan.projects.nav.*
Rename Nav{Section=>igation}, introduce Section enum
Move sagan.{support.nav=>blog.support}.SiteUrl
Add class-level Javadoc for sagan{|.team|.tools}.*
Add min-height so table doesn't break when downloads only have 1 row
Merge pull request #398 from spring-io/fix-tools-download-table-vertical-sizing

Add min-height so table doesn't break when downloads only have 1 row
Document and refactor sagan.support.nav.*
Add class-level Javadoc for sagan.blog.support.*
Add class-level Javadoc for sagan.blog.*