1. Sphinx 1.8 introduced [1] the '--keep-going' argument which, as its name
suggests, keeps the build running when it encounters non-fatal errors.
This is exceptionally useful in avoiding a continuous edit-build loop
when undertaking large doc reworks where multiple errors may be
introduced.
2. Remove the unnecessary blank line for tox.ini
[1] https://github.com/sphinx-doc/sphinx/commit/e3483e9b045
Change-Id: Ie837d376bb1a1d93367369d25140dd8a9d5ac14e
c61d73d902