Bug 20443: Fix POD

Bug 20443: Fix POD

Fixes the following failures:

 FAIL	Koha/Patron/Attribute.pm
   FAIL	  pod
		*** ERROR:
		empty =head3

		 in file Koha/Patron/Attribute.pm

		*** ERROR:
		empty =head3

		 in file Koha/Patron/Attribute.pm

 FAIL	Koha/Patron/Attributes.pm
   FAIL	  pod
		*** ERROR:
		empty =head3

		 in file Koha/Patron/Attributes.pm

   FAIL	  pod coverage
		POD is missing for merge_with
		POD is missing for object_class

 FAIL	Koha/Patrons.pm
   FAIL	  spelling
		 paramter  ==> parameter

except the missing pod for object_class, not needed.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>