Create the Reference FMUs used to introduce synchronous clocks.

[clagms]

As suggested by @andreas-junghanns in https://github.com/modelica/fmi-standard/pull/1143#pullrequestreview-478153037 , we should validate the example used to introduce synchronous clocks (see https://github.com/modelica/fmi-standard/issues/1073) by creating those FMUs in the Reference FMUs.

[andreas-junghanns]

@t-sommer : Can you have a look and turn the example in the text into a Reference FMUs? Cláudio will work on other issues in the standard next.