added support for custom group results checking

 * TODO:
  * added 'FIXME:' entry to describe an existing issue with the new
     "group results checking" feature (if used with "suite results
     checking").  Whilst not strictly a bug, the feature would be useful
     to library/test maintainers;

 * test/common.vim:
  * added support for custom group results checking;

 * test/vimrc_10_selftest-ex-local-pass.vim:
  * improved to take advante of this new feature;
  * renamed test-local variables;
test/*: added auto propagation of custom group results to its suite

 * TODO:
  * removed 'FIXME:' entry (as it is now implemented);

 * test/bin/run-tests.sh:
  * updated to match new tag format (minor change);
  * updated "example" lines;

 * test/common.vim:
  * added support for automatic propagation of custom group results to
     its suite;
   * new suite ("global") control variables;
   * new functions to reduce maintenance costs
      (s:EVLibTest_Suite_InitLow());
  * minor renaming of variables to improve readability;
  * EVLibTest_Finalise(), EVLibTest_Group_End():
   * added support for new EVLibTest_Gen_OutputTestStats() parameters
      (including logic to conditionally add "output tags");
  * EVLibTest_Gen_OutputTestStats():
   * refactored logic;

 * test/vimrc_10_selftest-ex-local-pass.vim:
  * heavily extended to support new "custom group results"
     functionality;
  * EVLibTest_Local_Test_10_2(): created;
   * turned a single test into 3, to cover all the possible "success"
      scenarios when using:
    * custom group results;
    * custom suite results;
    * (automatic propagation of custom group results to its suite);