Allow twarc to run as module

[igorbrigadir]

following on from #441 (comment)

It's possible to make it so that these commands are equivalent:

twarc2 version
python -m twarc2 version
twarc2.exe version

twarc version
python -m twarc version
twarc.exe version

I'm not sure how generally useful this is but i found it helped because i could run a profiler (slightly) easier, for example:

python -m cProfile -s cumulative -m twarc2 csv big_test.jsonl big_test.csv

It's not a terribly critical improvement either way, but it was a very small change with some boilerplate files.

[edsu]

That is super elegant @igorbrigadir!