Documentation for SQL features should reflect current standard

We document Derby as an SQL-92 database. This standard is now very old, and we should describe how Derby conforms to the most current standard (SQL:2011). Knut Anders Hatlen listed the relevant features in a comment to DERBY-6605.

This will involve at a minimum replacing the "Derby support for SQL-92 features" topic (http://db.apache.org/derby/docs/10.10/ref/rrefsql9241891.html) with a new one that describes Derby's support for current features, with notes as needed indicating when the support is partial. Only features Derby supports, fully or partially, should be listed. We should state that features not listed are not supported.

The information would be taken from http://wiki.apache.org/db-derby/SQLvsDerbyFeatures (which currently goes only through the 2003 standard). Listing the Feature IDs in the documentation would also be helpful.

Other topics should be changed as needed. For example, is the term "SQL92Identifier" still correct?