Feature - #296 Setting configuration variables in .taskrc

- Now supports 'task config name value', 'task config name ""', and
  'task config name' to directly modify the .taskrc file.
- Updated man page.
- Added unit tests.
- Modified existing config command to also display configuration
  variables that have no values.

src/Config.cpp

@@ -271,7 +271,10 @@ void Config::load (const std::string& file, int nest /* = 1 */)
 
   // First time in, load the default values.
   if (nest == 1)
+  {
     setDefaults ();
+    original_file = File (file);
+  }
 
   // Read the file, then parse the contents.
   std::string contents;