contrib: update copy-docs script to use rsync
Closes
cd docs &&
rm -rf build &&
make html &&
-cp -r build/html/* ../../jsonpickle.github.com
+rsync -avrP \
+ --delete \
+ --exclude=.git \
+ --exclude=.gitignore \
+ --exclude=.buildinfo \
+ build/html/ ../../jsonpickle.github.com/
