Add a simple command line interface

[jaimeMF]

Can be run as 'pycaption' or by calling 'python -m pycaption'

[vladiibine]

Hi,
Thanks for your contribution. We haven't merged your PR yet because we're currently in the process of restructuring pycaption a little. This will affect any command line clients, because the reader/writers will now support some additional (and important) arguments. Haven't thought of a nice generic way of supporting these arguments yet, so we'll postpone adding a cli to pycaption for the given time.

I use my own (forked) library as a cli for this library at this moment (https://github.com/vladiibine/pycaption-cli), but that is only because as I said, we don't have a better way to integrate the new parameters that will be used in a future version.

[jaimeMF]

Thanks for the comment, I'll take a look when the new version is released.