Syntax highlight (#141)

Adding GitHub syntax highlighting for the .pf test files and some
additional attributes for Fortran and C++ files.

.gitattributes

@@ -0,0 +1,55 @@
+# Handle line endings automatically for files detected as text
+# and leave all files detected as binary untouched.
+*     text=auto
+
+# Sources
+*.c     text diff=cpp
+*.cc    text diff=cpp
+*.cxx   text diff=cpp
+*.cpp   text diff=cpp
+*.cpi   text diff=cpp
+*.c++   text diff=cpp
+*.hpp   text diff=cpp
+*.h     text diff=cpp
+*.h++   text diff=cpp
+*.hh    text diff=cpp
+
+# Compiled Object files
+*.slo   binary
+*.lo    binary
+*.o     binary
+*.obj   binary
+
+# Precompiled Headers
+*.gch   binary
+*.pch   binary
+
+# Compiled Dynamic libraries
+*.so    binary
+*.dylib binary
+*.dll   binary
+
+# Compiled Static libraries
+*.lai   binary
+*.la    binary
+*.a     binary
+*.lib   binary
+
+# Executables
+*.exe   binary
+*.out   binary
+*.app   binary
+
+# Fortran files
+*.f   text diff=fortran
+*.for text diff=fortran
+*.f90 text diff=fortran
+*.f95 text diff=fortran
+*.f03 text diff=fortran
+*.pf  text diff=fortran
+
+# Enable syntax highlighting for files with `.pf` extensions.
+#
+*.pf linguist-language=fortran-free-form
+*.pf linguist-detectable=true
+*.pf linguist-documentation=false