Improved XML validation, examples & FMI 3 support, CVode 5.0

This release re-adds the pre-compiled SUNDIALS libraries and has no functional changes w.r.t. v0.2.15.

v0.2.15 (2019-12-18)

• FIXED validation of structured variable names with apostrophes
• FIXED dimensions of variables in FMI 3
• NEW validation of "flat" variable names
• UPDATED FMI 3 schema files
• UPDATED CVode 5.0
• IMPROVED optional files added to CMake projects for source FMUs
• IMPROVED NULL pointers are now ignored in freeMemory()
• IMPROVED frequently used utility functions are now imported to fmpy module
• IMPROVED parameter_variation adapted to new Dask versions