pg: Add date type & httpdate tests

...I was hoping not to have to implement the date type, because date
conversions suck, but it turns out manned.org actually needs it.
(Only to then convert it into a Unix timestamp again, hmm, maybe this
string conversion isn't useful at all?)

FU/Pg.pm

@@ -570,6 +570,11 @@ represent that without loss for dates that are near enough to the epoch (still
 seems to be fine in 2025, at least), but this conversion may be lossy for dates
 far beyond or before the epoch.
 
+=item date
+
+Converted between strings in C<YYYY-MM-DD> format. Postgres accepts a bunch of
+alternative date formats, this module does not.
+
 =item json / jsonb
 
 These types are converted through C<json_parse()> and C<json_format()> from
@@ -599,7 +604,7 @@ These are converted to and from hashrefs.
 
 =item money
 
-=item date / time / timetz
+=item time / timetz
 
 =item bit / varbit