Add .gitattributes file to fix linguist issues in repo

toroidal-code · toroidal-code · commit 08e14ac9a2ed · 2016-04-26T14:02:07.000-04:00
diff --git a/.gitattributes b/.gitattributes
@@ -0,0 +1,6 @@
+include/cxx-prettyprint/* linguist-vendored
+include/optional/* linguist-vendored
+gh-pages/* linguist-vendored
+CMake/* linguist-vendored
+doxygen_extras/* linguist-vendored
+docs/* linguist-documentation
