doc2dash silently fails with no output and success exit code

[ssbarnea]

I got a big surprised on CentOS where running doc2dash proved to return 0 and do nothing, regardless even creating any docset.

• happened even if the source folder didn't exist
• happend when source folder existed and had content but generated nothing.

Example:

    # inside almost any python package repo run
    PACKAGE=`python setup.py --name`
    pip install -q --user doc2dash
    tox -e docs
    python -m doc2dash -n $PACKAGE docs/build/html

I discovered that this happens when doc2dash is called as a python module, python -m doc2dash ignores any cli parameters, so doing nothing.