deleted references to other Axis, CoordinateSystems
deleted references to other Axis, CoordinateSystems

fixed reorder so that uses the compose method and should work for curvilinear ones as well (to be tested with polarcoords)

from_start_step, and identity cleanup

alexis-roche/nireg,alexis-roche/niseg,bthirion/nipy,alexis-roche/niseg,arokem/nipy,bthirion/nipy,bthirion/nipy,nipy/nipy-labs,arokem/nipy,nipy/nireg,alexis-roche/register,alexis-roche/nireg,alexis-roche/nipy,arokem/nipy,arokem/nipy,alexis-roche/nipy,alexis-roche/nipy,alexis-roche/nipy,nipy/nipy-labs,alexis-roche/register,bthirion/nipy,alexis-roche/register,nipy/nireg