Update the FAQ for Derby 10.5

The FAQ at http://db.apache.org/derby/faq.html should be updated for Derby version 10.5.

At least the following two entries should be updated:

• 4.7. Does Derby have a mode that causes it to run entirely in memory?
• 5.2. Does Derby support a LIMIT command?

We may also want to add more recent news for these:

• 5.3. Why do I get the error 'schema does not exist'? [is this an issue still?]
• 5.5. Can Derby generate unique identifiers like sequences?

Finally, a general task:

• Update links to the 10.2 docs to a newer revision [where appropriate], i.e. the 10.5 docs or even the trunk?

There may be more items to fix.