Enhancement - related to, but not fixing bug #293

- Added new attribute modifiers 'word' and 'noword' which find the existence
  of whole words, or prove the non-existence of whole words.  If a task has
  the description "Pay the bill", then "description.word:the" will match, but
  "description.word:th" will not.  For partial word matches, there is still
  "description.contains:th".
- Added unit tests for the text.cpp functions.
- Added unit tests including the new modifiers in filters.
- Added unit tests to parse the new modifiers.
- Modified man page.
- Modified the Context::autoFilter processing to use the new modifiers for
  +tag and -tag filtering.
- Added a support email to an error message, while looking at the filter code.
- Added new modifiers to the help report.
- Modified a utf8.t unit test to include an alphanumeric tag, rather than a
  smiley face.

src/tests/utf8.t

@@ -65,8 +65,8 @@ qx{../task rc:utf8.rc add project:Çirçös utf8 in project};
 $output = qx{../task rc:utf8.rc ls project:Çirçös};
 like ($output, qr/Çirçös.+utf8 in project/, 'utf8 in project works');
 
-qx{../task rc:utf8.rc add utf8 in tag +☺};
-$output = qx{../task rc:utf8.rc ls +☺};
+qx{../task rc:utf8.rc add utf8 in tag +Zwölf};
+$output = qx{../task rc:utf8.rc ls +Zwölf};
 like ($output, qr/utf8 in tag/, 'utf8 in tag works');
 
 # Cleanup.