doc: vale fixes, update TAL repeat object section. For repeat object/variable, added back first() and last() methods now that they are fixed. Moved start/end properties to separate property table along with index. Added details on how even works (e.g. even() is True when number() is 1 because the index is 0 which is even). Document returns from methods are mostly truthy and not true.

License
=======

Roundup is Free Software under the following license (from the file
COPYING.txt in the software distribution):

.. raw:: html

   <div class="file_insert">

.. include:: ../COPYING.txt

.. raw:: html

   </div>