Feature #298 - Configurable recurring task count

- Added new recurrence.limit value (default 1) to control the number of
  future pending tasks generated from a recurring parent task.
- Added unit tests.
- Updated taskrc man page.

src/command.cpp

@@ -640,7 +640,7 @@ int handleShow (std::string &outs)
       "next project shadow.command shadow.file shadow.notify weekstart editor "
       "import.synonym.id import.synonym.uuid complete.all.projects "
       "complete.all.tags search.case.sensitive hooks active.indicator tag.indicator "
-      "recurrence.indicator "
+      "recurrence.indicator recurrence.limit "
 #ifdef FEATURE_SHELL
       "shell.prompt "
 #endif