added capability of handling FreeCAD files with git diff

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "zsh/.oh-my-zsh/custom/plugins/zsh-syntax-highlighting"]
 	path = zsh/.oh-my-zsh/custom/plugins/zsh-syntax-highlighting
 	url = https://github.com/zsh-users/zsh-syntax-highlighting
+[submodule "git/zippey"]
+	path = git/zippey
+	url = https://bitbucket.org/sippey/zippey.git

git/.gitattributes

@@ -0,0 +1,2 @@
+*.FCStd filter=zippey
+*.FCStd diff=zip

git/.gitconfig

@@ -5,3 +5,10 @@
 	helper = store
 [http]
 	sslVerify = true
+[diff "zip"]
+	textconv = unzip -c -a
+[core]
+	attributesfile = ~/.gitattributes
+[filter "zippey"]
+	smudge = ~/zippey/zippey.py d
+	clean = ~/zippey/zippey.py e