Add FTPS support (#33)

[RachitSharma2001]

Title

Support for reading and writing files directly to/from ftps (ftp with tls)

Motivation

I have previously added support ftp servers (without tls encryption). Now, to add more complete ftp functionality, I have added support for ftp+tls servers.

from smart_open import open
with open('ftps://user:password@host:port/dir1/dir2/file') as fin:
     for line in fin:
          print(line)

Tests

I have edited the ftp integration tests to run an ftp and ftps server on different ports and then test reading, writing, and appending to each of them. (specific integration test here, pull up ftp and ftps servers here).

[piskvorky]

Looks good but can you look into not requiring & running that external Docker image for the testing?

If you could fix that we'll include this PR in the upcoming smart_open release (next week or so). Thanks.

[piskvorky]

Running external docker images is scary, both from security and also maintenance perspective.

Any way to launch the FTP(S) server directly from Python here?

[RachitSharma2001]

Thank you for letting me know. I have removed the docker dependency and instead directly set up the ftp and ftps servers on ci using the vsftpd linux tool. Let me know if this looks good or if there is anything else I should add or change.

[piskvorky]

Thanks for the quick resolution @RachitSharma2001.

@mpenkov can you please review?

[mpenkov]

Thank you for your work @RachitSharma2001 !