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.

#!/usr/bin/env python

# Roundup requires Python 2.7+ as mentioned in doc\installation.txt
from __future__ import print_function
import sys

VERSION_NEEDED = (2, 7)

if sys.version_info < VERSION_NEEDED:
    print("Content-Type: text/plain\n")
    print("Roundup requires Python %s.%s or newer." % VERSION_NEEDED)
    sys.exit(0)