Fix fetch first rows only grammar

After some additional test for #476 and more checking with the source
code I found out that I make a mistake in the grammar. The
MySQL/Postgres and the Derby/Oracle syntax should be different
productions.

Document fetch first row(s) only

Fix doc generation

In order to make the doc generation for #476 working I had to fix some
errors in existing files. These cover

 - lines which are too long
 - incorrect indentation
 - invalid markup
 - missing javadoc

Since 1.4.177 H2 supports FETCH FIRST x ROW ONLY however this is not
reflected in the grammar documentation. This covers all the variations
of the syntax.

There are 3 `help.csv` but I believe I got the right one. Some of the
checked in files seem to have been automatically changed and I don't
know if I should have committed those as well.

Fixes #475

Add alias for RANDOM_UUID

Fixes h2database/h2database#467 Deadlock between Sequence.flush() and…

* Custom data types handler

* Updated doc, changelog, dictionary. Fixed review comment.

* Extended the custom types handler interface

* Fixed test

* Fixed review comments

* Added note on ABI stability of the feature to docs

to make it more obvious

Updated commercial support information

Use System.nanoTime() to check timeouts