Merged in trunk updates into 2.0.x branch. See #3018
FMIL: Updated Readme file with current date. See #3018
FMIL: Add a comment to the build script and fix a documentation mistake in src/Util/include/FMI2/fmi2_xml_callbacks.h, for #3236
FMIL: Merge 2.0.x branch back into trunk for #3236 (2.0.x was slightly ahead)
FMIL: update FMI headers in ThirdParty/FMI/default/FMI2/ to FMI2.0rc1 headers for #3241.
Fix the corresponding discrepancies that showed up:
 * `fmiCompletedIntegratorStep` changed prototype
 * Updated contents of struct `fmiEventInfo`
Since the code almost does not use the FMI headers, this leaves almost everything working like before.
FMIL: Merge `fmiInstantiateModel` and `fmiInstantiateSlave` to `fmiInstantiate`, and same with `fmiFreeModelInstance` etc, for #3241.
The new `fmiInstantiate` takes an additional argument of type fmiType; mirror typedef added to fmi2_functions.h.
FMIL: Update comments etc. in FMI2 directories to state FMI version 2.0 instead of 1.0, for #3236
FMIL: rename `fmiGetNominalContinuousStates` to `fmiGetNominalsOfContinuousStates` for #3241