pg: Minor docs + tests

FU/Pg.pm

@@ -105,6 +105,15 @@ Connection is dead or otherwise unusable.
 
 Set the default settings for new statements created with B<< $conn->q() >>.
 
+=item B<< $conn->cache_size($num) >>
+
+Set the number of prepared statements to keep in the cache. Defaults to 256.
+
+Setting this (temporarily) to 0 will immediately reclaim all cached statements.
+Prepared statements that still have an active C<$st> object are not counted
+towards this number. The cache works as an LRU: when it's full, the statement
+that hasn't been used for the longest time is reclaimed.
+
 =item B<< $conn->disconnect >>
 
 Close the connection. Any active transactions are rolled back and any further
@@ -455,7 +464,7 @@ as well.  Much older versions will certainly not work fine.
 =item * Only supports the UTF-8 encoding for all text strings sent to and
 received from the PostgreSQL server. The encoding is assumed to be UTF-8 by
 default, but if this may not be the case in your situation, setting
-`client_encoding=utf8` as part of the connection string or manually switching
+C<client_encoding=utf8> as part of the connection string or manually switching
 to it after C<connect()> is always safe:
 
   my $conn = FU::Pg->connect('');