TDB2

- Implemented CmdAdd.cpp and CmdLog.cpp using TDB2.
- Implemented simple append writes in TDB2.
- Modified CmdImport to accept and parse JSON.
- Added more const-ness in DOM, Expression and Task, to allow TDB2::get_tasks
  to return a const vector ref, which is a Very Good Thing.
- Corrected usage for the export command.
- Implemented Task::urgency as a call to Task::urgency_c, which is a const
  overload to allow urgency calculations (without caching) for const Task
  objects.
- Removed obolete code from TDB.
- Added lots of diagnostic output for TDB2 - it's annoying, but will be
  gone soon.
- Added mention in CmdHelp of the new <filter> and <modifications>
  syntax elements.  Needs more.
- Added Command::filter overload which uses TDB2.  Not in use yet.

src/commands/CmdLog.cpp

@@ -51,12 +51,6 @@ int CmdLog::execute (std::string& output)
 {
   int rc = 0;
 
-  // Must load pending to resolve dependencies, and to provide a new ID.
-  context.tdb.lock (context.config.getBoolean ("locking"));
-
-  std::vector <Task> all;
-  context.tdb.loadPending (all);
-
   // Every task needs a UUID.
   Task task;
   task.set ("uuid", uuid ());
@@ -82,13 +76,10 @@ int CmdLog::execute (std::string& output)
 
   // Only valid tasks can be added.
   task.validate ();
-
-  context.tdb.add (task);
+  context.tdb2.add (task);
 
   context.footnote (onProjectChange (task));
-
-  context.tdb.commit ();
-  context.tdb.unlock ();
+  context.tdb2.commit ();
 
   if (context.config.getBoolean ("echo.command"))
     output = std::string (STRING_CMD_LOG_LOGGED) + "\n";