Keep build dir tidy by relocating Fortran modules

If we are building in-source, we don't want to have a bunch of output
files in the root directory; instead we put them in CMakeFiles/ where
all the rest of the object files go.

CMakeLists.txt

@@ -67,6 +67,7 @@ include (UseDynamicBoost)
 # put libraries in lib/
 set (CMAKE_LIBRARY_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}/lib")
 set (CMAKE_RUNTIME_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}/bin")
+set (CMAKE_Fortran_MODULE_DIRECTORY "${PROJECT_BINARY_DIR}/CMakeFiles")
 
 # find all the source code (note that these variables have name after
 # the target library and not the project). the documentation recommends