changed oF/addons to a C project for eclipse

addons is still no C project for eclipse. this way it isn't possible to rebuild the index or to use code completion, call hierarchy or symbol following in its full capacity.

I always import from "existing code as makefile project" instead of "existing projects ..." when it comes to oF/addons. I'm using the Linux GCC Toolchain for the indexer.

for me it works fine but I have to rebuild the indexer from time to time.