rip apart lxml in favor of hacky non standards compliant std python xml
remove lxml dependance, xdmf is now supported with default python xml lib

this means fewer xml files will work, but there is no lxml dependance. lxml can be put back
if i can hack in the ability to gracefully ignore xincludes of files that don't exist, that would
ensure the same behavior regardless of xml lib used, and therefore be transparent to the
end user
refactor spill -> print_tree
check in cython compiled c files, and remove cython from explicit dependancies

this also adds the build commands dev and devclean for convenience to always use cython