README.links to explain xref properly.

The array containment operators now behave per mathematical expectation
for empty arrays (ie, an empty array is contained in anything).
Both these operators and the query_int operators now work as expected in
GiST and GIN index searches, rather than having corner cases where the
index searches gave different answers.

Also, fix unexpected failures where the operators would claim that an array
contained nulls, when in fact there was no longer any null present (similar
to bug #5784).  The restriction to not have nulls is still there, as
removing it would take a lot of added code complexity and probably slow
things down significantly.

Also, remove the arbitrary restriction to 1-D arrays; unlike the other
restriction, this was buying us nothing performance-wise.

Assorted cosmetic improvements and marginal performance improvements, too.

Block elements with verbatim formatting (literallayout, programlisting,
screen, synopsis) should be aligned at column 0 independent of the surrounding
SGML, because whitespace is significant, and indenting them creates erratic
whitespace in the output.  The CSS stylesheets already take care of indenting
the output.

Assorted markup improvements to go along with it.

the <@ and @> operators.  These are not in fact equivalent to the built-in
anyarray operators of the same names, because they have different behavior for
empty arrays, namely they don't think empty arrays are contained in anything.
That is mathematically wrong, no doubt, but until we can persuade GIN indexes
to implement the mathematical definition we should probably not change this.
Another reason for not changing it now is that we can't yet ensure the
opclasses will be updated correctly in a dump-and-reload upgrade.  Per
recent discussions.

don't cause confusion with the built-in anyarray versions of those operators.
Adjust the module's index opclasses to support the built-in operators in place
of the private ones.

The private implementations are still available under their historical
names @ and ~, so no functionality is lost.  Some quick testing suggests
that they offer no real benefit over the core operators, however.

Per a complaint from Rusty Conover.

Per suggestion from Ron Mayer.

Fix lots of bad markup, bad English, bad explanations.

Second round of commits.  pgcrypto and pgstandby still to go...

the former README files.  Albert Cervera i Areny

or will never be converted.