Regexes

- Added regex support to substirutions.
- Fixed bug that prevented 1.9.4 from shipping with regexes.  If the
  description is "aXXaaXXa", and the substitution is /XX/.../ then the
  first substitutions changes the length of the string to "a...aaXXa"
  and therefore invalidates the index for the second match, and makes
  this change: "a...a...Xa".  The fix is to keep a running 'skew' count
  of the difference in 'from' and 'to' length, to adjust the match
  indexes.
- Moved the helper deltaSubstitutions function into the Task object,
  which makes more sense.
- Cleaned up output composition for CmdAdd.
- Eliminated #ifdef FEATURE_REGEX.  They are here to stay.

src/Task.h

@@ -81,6 +81,8 @@ public:
   void getDependencies (std::vector <int>&) const;
   void getDependencies (std::vector <std::string>&) const;
 
+  void substitute (const std::string&, const std::string&, bool);
+
   void validate () const;
 
   float urgency ();