RFR: JDK-6251738: Want a top-level summary page that itemizes all spec documents referenced from javadocs (OEM spec)

[Jonathan Gibbons]

Please review the code and tests to add support for a new `@spec url title` tag to javadoc.  Note, this does not include any changes to API doc comments to use the new tag in JDK API documentation; that will come later.

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Commit messages:
 - fix whitespace and position of HtmlStyle.refList
 - fix whitespace
 - JDK-6251738: Want a top-level summary page that itemizes all spec documents referenced from javadocs (OEM spec)

Changes: https://git.openjdk.java.net/jdk/pull/8439/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8439&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-6251738
  Stats: 1539 lines in 41 files changed: 1506 ins; 3 del; 30 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8439.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8439/head:pull/8439

PR: https://git.openjdk.java.net/jdk/pull/8439