Enable starting with python -m vitables

[mivade]

This is motivated by the vitables command seemingly not working on Windows, and it's easier to to do python -m vitables than have to remember that it should be python -m vitables.start.

[uvemas]

That is strange. The command works fine on my Windows 10 box. But I'll merge anyway.

[ankostis]

The problem on Windows is that you don't see any broken dependencies that prevent it from starting.
For example on my machine, i'm getting a DLL error when loading numexpr, but logging is hidden when launched through gui_scripts setuptools entrypoint.

In general i ha dnever had a good experience with the gui_scripts (e.g. STDIN/STDOUT are missing and exceptions raised when accessed are simply lost).

So maybe use 'console_scripts' instead?
Should i open a new PR for that?

[uvemas]

Please, proceed with the PR if you want and I'll merge it.