Commands

- Implemented CmdHelp object that replaces the report.cpp longUsage
  function, and builds the output dynamically from other Command
  objects.  This is also why the help text right now is very short,
  as only a few commands are migrated.
- Obsoleted longUsage function.
- Updated task.1 man page with 'execute' command details.
- Modified command.lua sample to include command usage.
- Removed "help" from old Context::dispatch, which means "help" is
  the first migrated command.
- Added usage and description to all Cmd* objects.
- Implemented Command::usage and Command::description as base class
  methods that simply return data that is specified by the derived
  classes.

src/main.h

@@ -99,7 +99,6 @@ int handleEdit (std::string&);
 
 // report.cpp
 int shortUsage (std::string&);
-int longUsage (std::string&);
 int handleInfo (std::string&);
 int handleReportSummary (std::string&);
 int handleReportCalendar (std::string&);