Download Reddit comments "as-needed"

[sabjoslo]

Add support to:

• Download Reddit comments to disk as-needed
• Clear them once the cleaned text has been written as a separate file

[sabjoslo]

@BabakHemmatian c6cab8 should fix this. Now Parse_Rel_RC_Comments and Parser take arguments download_raw and clean_raw, which, if True, will (respectively) download the raw data and clean it up once it's finished parsing it. Important: The biggest data files (~7.4 GB) have an eta of about an hour and a half to download.

A couple other things:

• In line 207 here, I changed the filename argument to BZ2File to path+filename. Right now, it seems like it assumes that you're working in the PWD, and I don't know if that was intentional on your part.
• I added some comments to Parse_Rel_RC_Comments explaining the new arguments. Feel free to change anything I got wrong there.

I did all this on a separate branch. If it works for you/there's nothing else you think should be changed, I'll merge it with the master branch.