Merge branch 'release/0.46.0' into develop
better tight layout fallback
kludgy support for plotting derived quantities
crd fixes and refactors
crd slicing fixes: fld[-1] was unruly before due to cell center slice sillyness
stop using deprecated plt.normalize
field wrap method returns a number if arr is just a 1 element ndarray, this is for ufuncs that reduce to a scalar
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
super preliminary support for multiprocessing streamlines
small mpl bugfixes (unbound vars)
clean trailing whitespace
make setup.py python 2.6 compatible
include active state ordered dict recipe for python 2.6 compatability
python 2.6 compatibility: remove xpaths in xdmf reader
quiet linter warning for relative import in xdmf
add changelog
small python3 compatibility changes