wabot/__init__.py defines def sessions(...) and also had a sessions.py
submodule, so wabot.sessions (attribute) resolved to the function,
shadowing the module for import wabot.sessions as m style access. This
is the same class of collision that browser.py -> _browser.py already
fixed. Renaming to _sessions.py removes the ambiguity and lets
docs/api.rst drop the :no-index: Sphinx workaround in favor of plain
autoclass directives on the public SessionRecord/SessionStore
re-exports.
