Add missing file extrarefs.bib

bibliography/extrarefs.bib

@@ -0,0 +1,19 @@
+% Additional references not part of OpenModelica, but used in the documentation.
+
+@misc{openmodelica.org:doc-extra:fmi1.0,
+  author = {{MODELISAR}},
+  title = {{Functional Mock-up Interface for Model Exchange 1.0}},
+  url = {https://svn.modelica.org/fmi/branches/public/specifications/v1.0/FMI_for_ModelExchange_v1.0.pdf},
+  month = jan,
+  year = {2010},
+}
+
+@
+
+@PHDTHESIS{openmodelica.org:doc-extra:cellier1979,
+  author = {Francois Edouard Cellier},
+  title = {Combined continuous/discrete system simulation by use of digital computers: techniques and tools},
+  year = {1979},
+  school = {ETH Zürich},
+  doi = {http://dx.doi.org/10.3929/ethz-a-000258490},
+}