FE function evaluation support
After the discussion with Nils, we came to the conclusion that adding support for the evaluation of discrete FE functions would be a great feature allowing easier implementation of variable stencils. However, the main difficulty will be the check if the current process "owns" all the data required to evaluate the function at a given coordinate. One also has to make sure that all the data of a function is synchronized across all processors. Since the evaluation will be called in the kernels, this synchronization should be done only once before calling the kernels.
Once this is done, adding the support of evaluating the derivatives should be straight-forward.