now replaces illegal windows filename chars w/ '_'
Closes issue #8

Merge branch 'iss8-WindowsFilenames'
Merge branch 'develop' for v2.0.0
Merge branch 'develop' -- include crucial file
Merge branch 'develop'
Merge branch 'develop': prepare for v2.3.1

+ multi-threaded downloading
  + specify number of threads with '-w N' or '--workers N' (default=8)

+ added option to create subdirectories for each tag line
  + enable with '-s' or '--subdirs' (default=False)

+ program no longer sorts the tags list, allowing for intelligent catch-all lines in tags.txt

- fixed bug that caused crash on tag lines with unicode
remove --subdirs and --workers args, put in cofig

- this closes issue #17
- also simplified argparse so make it more clear it just gets the
  verbosity level, hopefully this will serve as a reminder next time I
  am included to add an option
- also renamed ['downloads'] --> ['download_directory'] for more clarity
- tweaked formatting of json.dump
now correctly detects already downloaded files

- closes issue #18
- also, clarified/simplified what happens when no suitable downloads were
  found during update
Merge branch 'iss17-ArgsInConfig' into develop
Merge branch 'iss18-FixDetection' into develop