Minor updates for C snippets.

C++ updates:

  * GtestFixtures template imrpoved
  * added `@brief` to all doxygen comments explicitly.
	* improved `// end of ...` for all functions, classes, and namespaces,
  * Fixed auto generation of argument comments.

C updates:

  * Fix tab indents in several macros
  * Fixed not correctly squashed snippets.
  * added Doxygen coments functions.