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.

from roundup.dist.command.build import build_message_files, check_manifest
from setuptools.command.install_lib import install_lib as base

class install_lib(base):

    def run(self):
        check_manifest()
        build_message_files(self)
        base.run(self)