BibSort: improved washers

* Improves speed and realiability of BibSort washers by properly
  exploiting textutils.decode_to_unicode() and
  textutils.translate_to_ascii() functions.

* Improves speed of textutils.translate_to_ascii().

* Makes unidecode dependency mandatory.

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>
1: D400 First line should end with '.', not 't'
4: I102 copyright year is outdated, expected 2014 but got 2012
28: D203 Expected 1 blank line *before* class docstring, found 0
31: D401 First line should be imperative: 'Test', not 'Tests'
31: D400 First line should end with '.', not 'd'
38: D203 Expected 1 blank line *before* class docstring, found 0
41: D400 First line should end with '.', not 'd'
49: D400 First line should end with '.', not 'd'
59: D400 First line should end with '.', not 'd'