add doc and added centered_grid type of SamplingGrid to grid.py
add doc and added centered_grid type of SamplingGrid to grid.py
alexis-roche/niseg,alexis-roche/niseg,alexis-roche/nipy,alexis-roche/nireg,arokem/nipy,alexis-roche/register,nipy/nipy-labs,arokem/nipy,alexis-roche/nipy,alexis-roche/nipy,alexis-roche/register,arokem/nipy,nipy/nireg,nipy/nireg,alexis-roche/nipy,alexis-roche/nireg,bthirion/nipy,nipy/nipy-labs,arokem/nipy,bthirion/nipy,bthirion/nipy,bthirion/nipy,alexis-roche/register