Highlight tags when the value is one character long.

Tags with a value of length 1 were not highlighted with the metadata color.

Compare:

http://pythex.org/?regex=\b\S%2B%3A[^%2F\s]\S%2B\b&test_string=star%3A1%0Astar%3A12&ignorecase=0&multiline=0&dotall=0&verbose=0

http://pythex.org/?regex=\b\S%2B%3A[^%2F\s]\S*\b&test_string=star%3A1%0Astar%3A12&ignorecase=0&multiline=0&dotall=0&verbose=0

topydo/lib/PrettyPrinterFilter.py

@@ -66,7 +66,7 @@ class PrettyPrinterColorFilter(PrettyPrinterFilter):
                     p_todo_str)
 
             # tags
-            p_todo_str = re.sub(r'\b\S+:[^/\s]\S+\b',
+            p_todo_str = re.sub(r'\b\S+:[^/\s]\S*\b',
                                 metadata_color + r'\g<0>' + color,
                                 p_todo_str)