Tentative support for multiple function output in XDMF
Move HDF5 files to subdirectory
Cleaned up XDMFExporter and added option to delete old files
Merge branch 'master' of github.com:CamelliaDPG/Camellia

Conflicts:
	src/IO/XDMFExporter.cpp
Merge branch 'master' of github.com:CamelliaDPG/Camellia