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)
Upgrade to Boot 1.1

This commit updates Sagan to use Spring Boot 1.1.

Sagan's direct use of Flyway has been removed in favour of using the
Flyway auto-configuration that was added in Boot 1.1. To limit the
required configuration the migration scripts have been moved to their
default location.

namingstrategy has been renamed to naming_strategy to allow it to bind
to the namingStrategy property. For consistency ddl-auto has been
renamed ddl_auto.