support pydoc

virtualenv normally breaks pydoc, but restores its functionality using a shell function named pydoc. cf. pypa/virtualenv#149
pypa/virtualenv@4b775b8 
pypa/virtualenv#262
pypa/virtualenv#265

Obviously that workaround won't work for anything that isn't bash or zsh.

As far as I know, the only way to restore 'pydoc' in virtualenvs is to have an actual script in the virtualenv. 
On most platforms, this is a +x file inside bin/ but it can be a python script with appropriate hashbang. 
On windows, this has to be in Scripts\ and it has to have an executable extension; without assuming changed settings this can't be a .py file, the most reasonable solution seems to be a .bat file.