Fix word recognition for spell checker, ignore active partial words

See PR olivierkes#651

This commit restores the functionality that prevents spell checking a
word that is being actively typed at the end of a paragraph.

The goals for the spell check word match regexp are:

A. Words should include those with an apostrophe
   *E.g., can't*
B. Words should exclude underscore
   *E.g., hello_world is two words*
C. Words in other languages should be recognized
   *E.g., French word familiarisé*
D. Spell check should include word at absolute end of line with no
   trailing space or punctuation
   *E.g., tezt*
E. Spell check should ignore partial words in progress (user typing)
   *E.g., paragr while midway through typing paragraph*

This commit addresses all five of the above goals.

HISTORY:
- See issue olivierkes#166 and commit 6ec0c19 in the 0.5.0 release.
- See issue olivierkes#283 and commit 63b471e in the 0.7.0 release.

Also fix minor incorrect utf-8 encoding at top of source file.

manuskript/ui/highlighters/basicHighlighter.py

@@ -1,5 +1,5 @@
 #!/usr/bin/python
-# -*- coding: utf8 -*-
+# -*- coding: utf-8 -*-
 
 import re
 
@@ -146,9 +146,12 @@ def highlightBlockAfter(self, text):
             textedText = text + " "
 
         # Based on http://john.nachtimwald.com/2009/08/22/qplaintextedit-with-in-line-spell-check/
-        WORDS = r'(?iu)(((?!_)[\w\'])+)'
+        WORDS = r'(?iu)((?:[^_\W]|\')+)[^A-Za-z0-9\']'
         #         (?iu) means case insensitive and Unicode
-        #                (?!_) means perform negative lookahead to exclude "_" from pattern match.  See issue #283
+        #              ((?:[^_\W]|\')+) means words exclude underscores but include apostrophes
+        #                              [^A-Za-z0-9\'] used with above hack to prevent spellcheck while typing word
+        #
+        # See also https://stackoverflow.com/questions/2062169/regex-w-in-utf-8
         if hasattr(self.editor, "spellcheck") and self.editor.spellcheck:
             for word_object in re.finditer(WORDS, textedText):
                 if (self.editor._dict