All regular expressions slayed once and for all

illegal characters are now removed from filenames with sexy, sexy list
comprehension
wicked-fast multi-threaded downloads.

closes issue #9
cleanups throughout
stop sorting to close issue #13
fixed issue #14, problem was missing str()
added --subdirs option, closes issue #15
Merge branch 'develop'
arg for number worker threads (closes issue #16)

also, cleaned up debug output a bit
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