Minor fixes

[mpenkov]

• Fix Add tests for #39 #47: added unit tests to cover absence of multiprocessing
• Fix Can't open S3 files with ?-like characters in name #285: handled edge cases in S3 URLs containing question mark (?)
• Fix No handlers could be found for logger "smart_open.ssh" #288: switched from logging to warnings
• Fix Package missing __version__ attribute #289: added __version__