Pg: Add "time" type, change default format of "date" type but support "$date_str"

Using a consistent numeric interpretation for timestamps, dates and
times simplifies a bunch of operations. It certainly simplifies
conversion between the Postgres formats.

FU/Pg.pm

@@ -638,8 +638,24 @@ stored in a 64-bit integer. If you prefer that, use:
 
 =item date
 
-Converted between strings in C<YYYY-MM-DD> format. Postgres accepts a bunch of
-alternative date formats, this module does not.
+Converted between seconds since Unix epoch as an integer, with the time fixed
+at C<00:00:00 UTC>. When used as bind parameter, the time part is truncated.
+This format makes for easy comparison with other timestamps, but if you prefer
+to work with strings in the C<YYYY-MM-DD> format instead, use:
+
+  $conn->set_type(date => '$date_str');
+
+Postgres accepts a bunch of alternative date formats for bind paramaters, this
+module does not.
+
+=item time
+
+Converted between floating point seconds since C<00:00:00>, supporting
+microsecond precision. This format allows for easy comparison against Unix
+timestamps (time of day = C<$timestamp % 86400>) and can be added to an integer
+date value to form a complete timestamp.
+
+(There's no support for the string format yet)
 
 =item json / jsonb
 
@@ -689,7 +705,7 @@ can work around.
 
 =item money
 
-=item time / timetz
+=item timetz
 
 =item bit / varbit