Added mumps.h in linear_algebra and mumps_testing directory (ready for review)

Author: Matteo-Coppellotti

.gitignore

@@ -10,6 +10,18 @@
 test/fdapde_test
 test/.cache
 test/build/
+
+# Mumps testing
+mumps_testing/mumps_fdapde_test
+mumps_testing/.cache
+mumps_testing/build/
+mumps_testing/data/build/
+mumps_testing/test_output.log
+
+!mumps_testing/CMakeLists.txt
+!mumps_testing/user_config.cmake
+!mumps_testing/data/CMakeLists.txt
+
 build/
 CMakeFiles/
 .DS_Store