Expressions

- Broke out expression handling into two distinct flavors: filter
  and expression.  Filters need lots of preparation and mapping,
  which includes implicit 'AND' operators, expansion of syntactic
  sugar like /pattern/ etc and evaluate to a Boolean.  Expressions
  are simpler wiht less preparation, and evaluate to a Variant.

src/commands/CmdLog.cpp

@@ -78,7 +78,9 @@ int CmdLog::execute (std::string& output)
   task.validate ();
   context.tdb2.add (task);
 
+/*
   context.footnote (onProjectChange (task));
+*/
   context.tdb2.commit ();
 
   if (context.config.getBoolean ("echo.command"))